Talk:Nickel–metal hydride battery/Archive 1

Future of Rechargable batteries
/Batteries can be very helpful. It can also make electromagnets There is Li-on which doesnt have Memory effect but those cant come in the standard AA/AAA format [the battery from my Camera doesnt work in my portable DVD player or laptop, more specific, man Henry Ford invented mass producution making things more universal and we switch back]. Will all electronic use Lion that wont be avaliable in a couple years?

Will AA and AAA batteries be around for a million years?

Requested move
The current article is about the nickel metal hydride battery, but the name only specifies what it is made out of. Other articles include "battery", such as lithium battery and lead-acid battery. -- Kjkolb 07:36, 26 December 2005 (UTC)

Voting

 * Add *Support or *Oppose followed by an optional one-sentence explanation, then sign your vote with ~ 
 * Support - seems a very obvious move. Rd232 talk 11:42, 27 December 2005 (UTC)
 * Support - makes it more obvious what the article is about. Lee J Haywood 12:52, 27 December 2005 (UTC)

Discussion

 * Add any additional comments

In the specifications, we have a couloumic charging efficiency of only 66%. It is referenced to a commercial site that sells batteries and chargers and while it seems informative, I would prefer better explanations. Other commercial sites actually put their chargers at much higher efficiencies, though I do not know that it is the couloumic charge efficiency. They just call it the charging efficiency. I found a place that might actually solve my question but I'm limited in my ability to get access. It is from an IEEE article Sept 2006 on NiMH and NiCd charging characteristics. Although references to 66% abound on the web, they basically go back to the same commercial site.

74.98.108.37 21:29, 11 December 2006 (UTC)

In the battery specifications table, it says that the energy/weight ratio can go up to 200 Wh/kg. I have been unable to find a NiMH battery with that kind of ratio. That would make the NiMH battery the same as the Lithium Ion battery!!! Could someone please give the true maximum with a reference. Thanks. (User:66.68.107.60)

How do you achieve a long time storage charge of around 40%?

What is the metal (besides nickel) in NiMH? What are the electrodes made of? -- Kaihsu 09:18, 2004 Jul 12 (UTC)

I feel that the qestion of what the Metal is, is so freaking important that it should be in the article until answered. Hackwrench, Robert Claypool (User:66.213.15.15)


 * See the talk below this. The other "metal" is hydrogen, stored as a metal hydride. And if the article didn't make this clear to you, we should fix the article.


 * Atlant 14:37, 10 August 2005 (UTC)

Earlier, Robert posted the following question in the article (which I've now excised to here):


 * Nobody seems able to explain what the "metal" in Nickel Metal Hydride is.

This resource claims that a variety of intermetallic compounds are used as the "metal" in the metal-hydride negative electrode and that the particular alloy is chosen for low equilibrium pressure, resistance to corrosion, mechanical stability, reversibility, hydrogen storage ability, and other factors. I suspect that any given battery design treats the electrode choice as a trade secret although it's obviously not a well-guarded one.

The upshot is that the particular metal isn't very important; hydrogen is the actual participant in the reaction.

I guess someone can edit the main article to include this data if they wish.

Atlant 17:44, 7 Mar 2005 (UTC)


 * Sure, sounds fun.--Joel 23:47, 25 May 2005 (UTC)

Result
moved. WhiteNight T 00:25, 30 December 2005 (UTC)

is there really a memory effect in NiCds
i have read that there is no memory effect in modern NiCds (there is a very little, almost undetectable memory effect in non-modern NiCds). when people who know nothing about batteries refer to the memory effect they are almost always refering to voltage depression. i think the part that they (Ni-mh batteries) don't suffer from the memory effect should be edited to say voltage depression instead of memory effect. ni-mh batteries, like NiCds do suffer from voltage depression if improperly charged (though significantly less than ni-cds) but there is no true memory effect in almost any modern battery. Another meaning of memory effect is: A battery rated 1000 miliamp hours will after several charge cyles of 100 milliamp separated by discharge cyles of 70 milliamps will now have a capacity of perhaps 200 miliamp hours meaning the battery remembers that you only want 70 milliamp hours and forgets that it was a 1000 milliamp battery. Lead acid batteries have very little memory, but nickle-cadmium batteries and some other types are best discharged until their terminal voltage drops to about 90% of the rated voltage before recharging. The 90% rule varies with number of cells in series and manufacture. Neil

I am just one person here, but here is my past 7-8 years experience of using NiMH. NiMH are very good at the start of their life cycle. They are Exceptional for powering medium drain devices, low drain devices seem to run just fine on NiMH for up to 2 years between recharging eg: remotes, 8 years ago I bought 12 AA NiMH batteries for use in GBA's and digital cameras, after 4 years the digital camera I was running would no longer run off NiMH unless they were charged the same day as used, and only for minutes of shooting/being turned on, to date the GBAs can run for hours, but not as many as when new, perhaps as many as 2 hours less run time 8 years later, and since the new Gameboys all have Li-ion, i have loads of old NiMH powering all my remotes, and enough to cycle charged with discharged quickly. Modern cameras might run longer, or perhaps modern NiMH are better, the NiMH batteries i got 8 years ago are rated as 1600, today i see as high as 2400 in stores, and the article references as high as 2500. Still, the batteries were used most often in gameboys, my dad also bought NiMH for his digital camera, and only used them with it, i don't know what they were rated as, but after 3-4 years he switched to alkaline batteries, and then finally bought a Li-ion powered camera. after a few years he was getting less battery life from NiMH than from alkaline batteries. Basically, in my experience, Ni-MH loose the ability to run high drain devices after 3-4 years, it happens no matter the make or rating, they just stop working in high drain devices, perhaps storing them in a freezer can offset this problem, but i wouldn't know, but i've seen websites that recommend freezing NiMH as long as you can thaw them without getting them humid prior to use. I know this from only 2 people really using NiMH batteries 'in real life' and i have no idea why the batteries stop running high drain devices, but they do. my dad might have gotten cheapo 1600 or 1800 NiMH too, so perhaps the 2400 devices don't have the same problem with digital cameras, or perhaps i had problems with reverse charging, but i don't know. Still, I've only had 2 NiMH batteries go completely bad in 8 years, (one in the charger, one while on a shelf) but everyone I've known who've used them in digital cameras loathed them, because the cameras needed new NiMH every 3 years. Kesuki (talk) 00:48, 15 May 2008 (UTC)

Capacity in Coulombs
Why is 1100 mAh and a 2500 mAh batteries 4C and 9C? Shouldn't they be 4kC and 9kC (1,1A * 60s*60s, and 2,5A * 60s*60s)?


 * Your analysis sounds correct to me. But if you edit the article, you may want to make sure that the two different uses of "C" are clearly distinguished. Right now, there's the use of "C" as "charge/discharge rate of the cell" (in the sense of "Charge at 1/10 C") and right near it, is "C" as Coulombs.


 * Atlant 13:08, 15 August 2005 (UTC)


 * They should be distinguished in part by the C for the quantity being always italic and the C for the unit of measure coulomb being always upright. Of course, the use of "20C" for temperature is also in need of changing; I'll fix that.  Gene Nygaard 12:54, 27 October 2006 (UTC)

In-Cell Charge Control (I-C3)
Does anyone have any info on this system? The batteries using this technology apparently has some kind of internal pressure sensor, allowing them to be charged in 15 minutes. I've searched around abit, but haven't found any detailed technical info. --GalFisk 20:00, 14 September 2005 (UTC)

A Google search shows that IC3 is/was patent pending by Rayovac. Maybe you could search out the patents. Efficacy 18:52, 28 September 2005 (UTC)

The technology behind I-C3 appears to be an internal pressure sensor. Presumably the sensor is measuring the pressure buildup due to gas formation. When the pressure is getting dangerous, the charger slows down, giving the battery a chance to deal with the gas, and then it reverts back to high speed charging. To eliminate the heat problem the charger uses a large high-speed fan. Even so, at the end of charging those damn batteries are just about too hot to handle. I really do like the system overall. The batteries work great. 71.0.197.147 19:52, 21 June 2006 (UTC)


 * I started the article on I-C3 with some information form the patent, and linked it from this article. --GalFisk 09:01, 28 May 2007 (UTC)

Stanley Ovshinsky
I've heard his claim that Stanley Ovshinsky invented nimh batteries, and there is some documentation of that (the wikipedia article on him desperately needs expanding.) I realize the true story may be more complex, but if he did invent them shouldn't it be mentioned here?

PS: His post is found under Stanford R. Ovshinsky, other forms of his name is Stan, Stanley, and Stanislav.

Invention of the NiMeHx battery technology: '''Please see the article below in "History ....". The invention and pioneering work goes back to 1964 at the Battelle Geneva Research Center.

Revertion justification
I reverted the image change. Copyrighted diagrams are just that and should not be used here when a free image is available. Of course anyone is free to use the information in that diagram and create a new and free diagram. Zeimusu | Talk page 13:49, 17 January 2006 (UTC)

Chemistry
Hi, does anyone know the chemical reactions (half-equations) that take place in a NiMH battery? If so, can it be added to the article? Neonumbers 07:21, 12 March 2006 (UTC)

Electrical characteristics
There's no mention of the cell voltage under various conditions. It would appear, for example, that freshly charged and unloaded, a 1.2V cell will give nearer 1.4V. That's a notable difference from NiCad. --82.69.188.246 23:36, 24 May 2006 (UTC)
 * Open-circuit (no-load) voltages don't mean much, though. As soon as you put a load on the cell, it goes back down to about 1.2 volts. —The preceding unsigned comment was added by 24.6.66.193 (talk • contribs).
 * If not left to sit too much, voltage with a 1A load should be closer to 1.24V, and if you apply a load of 0.1A on a fresh cell, it's voltage stays above 1.3V for a considerable time. Note that I have an el'cheapo blinking bike light that drives three low power white-ish LEDs, and (unofficially) runs on 2 AAA NiMH when fresh (>1.25V-1.3V). In the said configuration, it runs for hundreds of hours at lowest power dancing-blinking, and for many days continuously at 50% blinking (progressively fading to an unacceptably low light level _of_course_). period. Actually, if you have a closer look at any manufacturers technical documents on their NiMH and Alkaline offerings, you can see that the discharge graphs of the two match pretty closely. So, if NiMH must be labeled 1.2V, Alkaline ought to receive a 1.3V label! bkil (talk) 15:02, 12 August 2008 (UTC)

Initial Charge Time
I've heard a number of places that one should initially charge a NiMH battery for a far longer period than on subsequent charging. Is this the case and, if so, then why?


 * No, just let your automatic charger charge it as per usual; it knows best.


 * Atlant 15:59, 30 August 2006 (UTC)


 * Uh, YES, this is called Pack forming and is a requirement in order to get the most out of NiMH battery packs if they will be "fast" charged. Failure to do so will result in having diminished capacity. The process involves charging the pack at charge rate of C/10 for a specific length of time, something like 20hours for a 2000mAh pack (at a rate of 200mA).
 * There is a ton of expert knowledge about batteries for (Radio Control applications) at [RC Battery Clinic]. This guy has years of experience in the field of batteries. - Gdavidp1 23:18, 7 September 2006 (UTC)


 * Opinions obviously vary. ;-)


 * Atlant 00:01, 8 September 2006 (UTC)


 * Well, actually it's not a question, you (or someone at the factory) must do a forming charge before use. There's no guarantee that fast charging works at all on fresh cells. It's been stated elsewhere, but I tried it myself. It happened to me a few times, that charging of cells that sit many years unused ended prematurely (after less than 15-30min). At each instance, I replugged them after verifying the premature nature of the charge (from temperature, OC/voltage, internal resistance) and they completed successfully. There may exists other more technical reasons (like degraded performance or cycle life), but this already ought to be enough for you. :) bkil (talk) 13:54, 12 August 2008 (UTC)

Temperature effects
NiMH are known to stop functioning below -10 degrees centigrade/fahrenheit --any confirmed views on this?
 * Beats me, but original individual research has concluded that high quality cells such as the Sanyo eneloop perform well down to -24 degrees Celsius. :) Also see the links. bkil (talk) 15:04, 12 August 2008 (UTC)

- I have also used NiMH cells at -25 C, 5 Degrees below the minimum recommended discharge temperature of various manufacturers. This was with Rayovac AA sold as D cells. I think they perform better than sealed lead-acid (0.5C/h draw). 208.99.137.71 (talk) 08:09, 25 January 2010 (UTC)

Patent ownership
Shouldn't the article say that the patents to NiMH technology are currently owned by Texaco/Chevron? Perhaps, but patents don't mean much any more. According to another reasonably credible wiki article, Panasonic will build a nickle metal hydride 300 volt battery to supply up to 200,000 watts to the two 100 kilowatt electric motors in a big Chevy truck which you can buy in the fall of 2007 The Wikipedia link has lots of details, most of which seem probable. I'm disapointed that cheap lead acid batteries likely will not be used, as the replacement cost of a high tech battery is too costly to risk letting the average driver plug it in. It looks like the system will be so complex that compentent mechanics will be unavailable when repairs are needed. A big Chevy truck instead of a Yukon will likely be the only hybred available from Chevy this year, possibly because the safety of the high tech battery will still be unknown by Oct 2007. The battery is less hazardous to the pasengers under the truck bed instead of behind the third bench. Neil —The preceding unsigned comment was added by 69.107.85.40 (talk • contribs).

Patent encumbrance of NiMH batteries In 1994, General Motors acquired a controlling interest in Ovonics's battery development and manufacturing, including patents and trade secrets controlling the manufacturing of large nickel metal hydride (NiMH) batteries. In 2001, Texaco purchased GM's share in GM Ovonics. A few months later, Chevron acquired Texaco. In 2003, Texaco Ovonic Battery Systems was changed to Cobasys, a 50/50 joint venture between Chevron and Energy Conversion Devices (ECD) Ovonics.[72] It has been argued that large-format NiMH batteries were commercially viable and ready for mass production, but that Chevron and other oil-related interests suppressed the technology to forestall the introduction of plug-in hybrids.[73] Plug-in hybrid

(It is kind of pathetic that the article currently has so little history info. And it is also sad to have nothing about the matter of usage of big NiMH batteries in cars possibly being suppressed by big corporations, as discussed in the Plug-in Hybrid article.)-69.87.200.161 17:31, 11 May 2007 (UTC)

Advertisement
This looks like an advertisement to me: "A new nickel metal hydride battery on the consumer market made by Sanyo, called eneloop, limits the self-discharge problem and retains energy by means of "superlattice alloy". Eneloop batteries retain 90% of their charge after six months, 85% after a year and 70% after two years. [1] They are estimated to last 1,000 cycles and have four times as much energy capacity as alkaline batteries."

Content was added by: 213.232.127.35 WolfKeeper 09:41, 17 November 2006 (UTC)

It doesn't necessarily seem inappropriate though; if the claims are true, it would probably be notable.WolfKeeper 09:41, 17 November 2006 (UTC)


 * I haven't tested the 1000 cycles claim yet (though it looks right), but the other features are indeed being enjoyed by us happy Eneloop owners! :), , ... bkil (talk) 15:15, 12 August 2008 (UTC)

History and other information
"NiMH battery technology was developed at the end of the 1980's and commercialised first by the Matsushita Company"

Moved from main page:

This is not true: NiMeHx battery technology was invented and in the pioneering stage developed already 1964 at the Battelle Geneva Research Center, Electrochemistry Division. Patent filed in Switzerland: 2.05.1967, equiv. filed on 24.04.1970 in US 3,669,745 (granted 13.06.1972. Inventor: Dr.-Ing. Klaus D. Beccu (Technical University Berlin). Further patents on Ti-Ni hydride alloy phases: US 3,824,131 (July 16, 1974)and in many other countries. The work was sponsored from early 1970 for over 14 years by the German automobile company Daimler-Benz that obtained all the patent rights. Through the many publications including the patents and scientific conferences this innovative energy storage system was known worldwide and attracted many companies to start research for further improvment of the alloy composition and metallurgical structure. The most successful company in this respect was Energy Conversion Devices (ECD) with its battery company Ovonics. Stan Ovshinsky, the owner of the company, and his team introduced a new microstructure concept and new metal alloys to further improve the specific electrode capacity, performance and lifetime. Their technology was licensed to a large number of battery companies worldwide including Matsushita. (contribution by Dr. K.D. Beccu, Geneva) —The preceding unsigned comment was added by 213.17.66.42 (talk) 17:49, 23 April 2007 (UTC).

Having worked at Energy Conversion Devices and Ovonic Battery Company, I'm aware that they did not invent the underlying technology, but rather developed, and hold many patents on, various active materials. The technology goes back to Edison, with the metal hydride electrode development having been developed in the fifties or sixties. Unfortunately, I'm not sure that I'm familiar enough with the history of the technology to do an accurate and well-sourced rewrite. How can we update the History section to be accurate? 70.90.142.202 12:26, 16 October 2007 (UTC)

The Battelle patents (developed for the German automotive company Daimler-Benz) filed in Switzerland, Germany, US and other countries from 1967 were very seriously examined in those countries and we had to go through the whole procedure in Germany and US with prior art citations raised especially by the German battery company VARTA. However, it was confirmed that VARTA's work had dealt only with the electrocatalytic effect of metalhydrides with superficially adsorbed hydrogen - not for interstitial hydrogen storage in big volumes. Thermal Hydrogen absorption /desorption effects on certain metals were earlier observed even before Edison but the problem is the electrochemical reversibility which we solved through Ti2Ni/TiNi alloy compositions. Conclusion: there is a significant difference between hydrogen adsorption and storage. - No doubt (as I said above), Ovonic has significantly improved the alloy composition and structure (disordered microcrystalline) and brought the system to commercialisation. Since I am a consultant to ECD/Ovonics I have several times discussed this subject with Stan Ovshinsky, Mike Fetcenko and Marv Siskind never Battelle's pioneering work and intellectual authorship was contested. Klaus D. Beccu / Battelle Geneva Research Center. —Preceding unsigned comment added by KDB196 (talk • contribs) 14:06, 30 October 2007 (UTC)

Maintenance and reforming
"Long-term maintenance charge of NiMH batteries needs to be by low duty cycle pulses of high current rather than continuous low current in order to preserve battery health."

"Brand new batteries, or batteries which have been unused for some time, need "reforming" to reach their full capacity. For this reason new batteries may need several charge/discharge cycles before they operate to their advertised capacity."

These are important, and perhaps dubious claims. The should be backed up with details and references.-69.87.204.120 14:24, 3 May 2007 (UTC)

The charging voltage is 1.4-1.6 V/cell. Duracell recommends "a maintenance charge of indefinite duration at C/300 rate". A fully charged cell measures 1.35-1.4 V (unloaded), and supplies a nominal average 1.2V during discharge, down to about 1.0V (further discharge may cause permanent damage). Voltage Depression ("Memory Effect") from repeated partial discharge can occur, but is reversible through charge cycling.  -69.87.204.120 15:06, 3 May 2007 (UTC)

Maximum capacity = 7000mAh???
The second paragraph states that the capacity of AA batteries can be as high as 7000mAh. I find that very hard to believe. The highest I recall having seen is 2500 mAh. Could someone in the industry please address this if required? Thanks. Xarqi 08:32, 19 July 2007 (UTC)

3000 mAh is readily available, but havn't seen anything higher. I call BS Towel401 (talk) 00:16, 20 September 2008 (UTC)

Low Self Discharge
I want to remove the section on "hybrids" and how they are used in marking these new cells. Only Rayovac is using the name "Hybrid" in marketing these cells, and only variant being "Hybrio" by Uniross. The paragraph takes issue with these marketing terms, and I agree that the marketing is hype, but I don't think it has to be discussed as a topic. Wikipedia is not for debunking marketing hype. Redfish2 14:42, 19 July 2007 (UTC)

Cold Fusion Tangent?
In my opinion the section "Security and Danger" needs a major re-write, focusing on the safety of using the batteries, not on unrelated hydrides.Oganocali 22:40, 20 August 2007 (UTC)

Very old threads here
What about archiving threads in this discussion that have been inactive for, lets say, a year? Please review the threads and you'll agree with me that this has become somewhat messy, with obsolete threads. This can be automatically done by MiszaBot, but I need consensus here. --Agent Fog 16:54, 30 August 2007 (UTC)


 * I cannot agree -- the total page is not that long so far, and it is more convenient to have the entire history here in one place. Otherwise, people are more likely to just repeat the same subjects, unaware... -69.87.204.176 22:46, 13 October 2007 (UTC)

Test results for LSD types
CandlePower Forums seems like the best source of detailed technical discussions, for low self-discharge NiMH batteries. Perhaps "standard" NiMH will die out and the LSD types will take over the market. Since the AA and AAA are the only sizes of LSD currently made -- to what extent are C and D sizes actually available of any type of NiMH? -69.87.204.16 13:51, 23 October 2007 (UTC)
 * Eneloop Self Discharge study
 * Eneloop AA are not that good due to reduced capacity
 * Technical comparison of NiMH batteries

SIZES

all-battery.com sells C 5000 mAh, D 10000mAh, 9V 250mAh, tabbed, and odder sizes: -69.87.199.6 (talk) 18:07, 25 November 2007 (UTC)

It seems that "most" C and D NiMH batteries are "fake" -- AA cores in a dummy shell. thomas-distributing.com is mentioned as a source of "real" C and D sizes. C and D sleeves are available for intentionally using AA batteries this way. Checking the rated capacity would be the way to know -- a rating around 2500 mAh means fake. C should rate 5000-ish, D 10000 or more. -69.87.202.109 (talk) 21:38, 28 November 2007 (UTC)

Charge/discharge efficiency
The "new" Duracell one-year LSD pre-charged 2000mA AA now carried at CVS in New England states on the package that a standard charge is 200mA for 16 hours -- a pretty poor charge/discharge efficiency. The article states in the infobox "Charge/discharge efficiency 66%". There should be more about this aspect in the article, what the range is for NiMH batteries under what conditions, and how this compares to other rechargeables. -69.87.199.159 18:11, 29 October 2007 (UTC)


 * That's about 62%, pretty standard with a safe amount of overcharging. I'd say 67% of efficiency is the right amount for C/10 charging, however, as I've heard quick chargers could reach at least 80%. Consider the following example calculation: Sanyo's specifications for it's C/3 MDR03W eneloop charger is given as follows: 600 mA @ 2.4V, 250 minutes of charge typical for the 2000 mAh eneloop. That turns out to be 2000 mAh / ( 600 mA * (250 min / 60 min/h) ) = 80%, and my prior experience with the former said confirm a figure like that. Others: [] bkil (talk) 14:50, 12 August 2008 (UTC)


 * I often find the Charge/Discharge efficiency for NiMH cells being misunderstood. I find two common mistakes. The first is ignoring or misunderstanding Peukert effects of discharging. The second is incorrectly including over charge Ah. A 10 mL glass will not hold more than 10mL, if I pour 1L at it I just make a mess and the 10mL glass is still only holding 10mL. The easiest method to see the effects of this is to conduct an experiment where you minimize those two influences. To minimize the Peukert effect discharge slowly, like C/10. Overcharging is included in most smart chargers, so we have to take a more active role. To minimize overcharge influences first determine how many Ah the battery will give you on a discharge cycle, preferably a repeatable result over 3 to 5 such efforts. Than apply slightly less Ah to the cell than you know you were able to get from it when it was 100% charged. I think 10% less is plenty and easy to do. So if I am testing a 2,000 mAh rated AA I first test it under the low discharge rate to minimize the Peukert effect and determine its true discharge capacity. Repeat 3 to 5 times to ensure consistent results. If it turned out to be ( for example ) 1,957 mAh I then charge this battery cell with 1,761 mAh. I know then that the amount of energy I applied to the cell is less than the amount the cell can hold. Then I do the slow discharge to again avoid/minimize Peukert effects. Then repeat this process until your Cycle Efficiency % is level and not changing. Each time you keep applying that same 1,761 mAh to the cell. Eventually you will reach a level point where you have more accurately determined the charge/Discharge Cycle Efficiency of the cell. Ideally all of this should be done at the same temperature to avoid temperature influences. When I have done this myself... I have not yet found a NiMH cell that is under 90% Cycle efficiency... and the highest I have found was ~95%... I have not yet found a published paper where this same work was done to site as a reference. But I do invite others with doubts to do the test themselves, or to point me to a NiMH cell that they did test correctly and that gave less than 90% cycle efficiency. [ooIamIan 1-16-10] —Preceding unsigned comment added by OoIamIan (talk • contribs) 18:04, 16 January 2010 (UTC)

Patents
I added a section: Patent Encumberance of NiMH batteries, copied from Wikipedia page about electric cars. I thought this was most relevant to this article. —Preceding unsigned comment added by Adinov (talk • contribs) 08:40, 13 November 2007 (UTC)

Full charge / over-charge
The article, and particularly the accompanying graph, are sadly vague about the details around being fully charged. No specific sources of such details are provided. And the referenced article about overcharging is very general.

As the battery is charged, at a constant current, the voltage rises. As the state of "fully charged" is approached, the voltage rises faster (more so than the graph shows). But as the state of full charge is then eventually reached and passed, into the overcharge zone, somewhere in there the voltage actually peaks and starts to go back down. This is odd behavior -- apparently not always terribly damaging. It would be good if the article would describe this zone in detail. In particular, what exactly is the chemistry doing, why does the voltage go down, and why is this not terrible?

Here are some specifics about full charge. In general, the charging voltage is (very) approximately 1.5V. Then, the peak voltage reached around full charge is about 1.5 to 1.7V, depending on the rate of charge and the temperature of the battery. Immediately after being charged, a fully charged NiMH battery measures about 1.44 to 1.45V during the first minute, open circuit. By about an hour later, it measures about 1.41V.

There may also be something strange about the temperature at the end of charging, perhaps connected to the voltage peaking. Using a slow dumb 50mA charger and old 1600mAh RS AA batteries, there is never a large increase in temperature, over ambient. During the early part of charging, there seems to be no perceptible increase. Some time around the completion-peak, the batteries (and charger) do warm enough to feel. But later, the steady-state over-charge condition seems to be not as warm. Why? How? -69.87.200.50 (talk) 03:22, 9 January 2008 (UTC)

- The voltage may be partially temperature dependent. At the end-of charge, the battery temperature rises noticeably, as you have mentioned. I'm sure there are electro-chemical explanations for the voltage dropping during (not after) overcharge (that I don't completely understand). You may want to research the related NiCd battery chemistry. If the reaction increases the internal resistance of the battery, it may reduce the current flow. 208.99.137.71 (talk) 07:51, 25 January 2010 (UTC)

Nimmer?
Regarding the anonymous edit to the first sentence on January 11th, does anyone actually pronounce NiMH as "Nimmer"? I can't help but think someone just made this up, as I've never heard them pronounced that way. A quick search on the net didn't turn up anyone else mentioning that pronounciation either. At the very least, they didn't provide a source, and I'm thinking they just fabricated it entirely.\

Cryoburner (talk) 20:24, 28 January 2008 (UTC)


 * Between my experiences in amateur radio and IT I have NEVER heard anyone pronounce NiMH as "nimmer" but rather ALWAYS as "nimm". I MOVE for the deletion of this pronunciation statement, and replacement with the "nimm" unless a dictionary-level source can be provided.Jo7hs2 (talk) 19:37, 1 February 2008 (UTC)


 * I thought it might make sense in British English, a non-rhotic pronunciation, but I’ve never heard of that, either. (Admittedly, neither have I heard nimm.) Google search shows nothing meaningful not copied from Wikipedia. I’m killing that shit accordingly. —Wiki Wikardo 20:39, 8 February 2008 (UTC)

Patent discussion
The discussion of patent restrictions on NiMH batteries is the stuff of very, very bad conspiracy theorists. It's routine for manufacturers of any product to refuse small orders, as they can seldom recover their line startup costs. The theory that evil Chevron is restricting access deserves a single sentence at best, and in a properly formed article would not even be mentioned. The presence of two lengthy paragraphs discussing the possibility without a single word of rebuttal compromises the objectivity of the entry. —Preceding unsigned comment added by Phil Weingart (talk • contribs) 12:41, 17 May 2008 (UTC)

maximum allowed non-repetitive peak current for an 5 msec pulse, or the maximum pulse lenght at 10C current?
If I power a device alternatively with AC/DC converter and NiMH batteries, then the batteries will load the converter's puffer electrolyte capacitor when I connect them. (short to ground trough capacitor) It means very high initial current. (4 AA's at 25mOhm AC impedance+ 10000uF el.cap. 65mOhm ESR +1/Cw +cables -> 5V/200 mOhm=25A) So what is the maximum allowed non-repetitive peak current for an 5 msec pulse, or the maximum pulse lenght at 10C current? I can't find it in specs. (86.122.102.192 (talk) 17:51, 16 June 2008 (UTC))

Charging
I plead for removal of the entire section because of insignificance to NiMH chemistry. The methods described are partially outdated and techniques should rather be looked up in the specific articles. (And those NiCd chargers not suited for NiMH will probably ruin any cell.)
 * Steffen Heinrich, 87.187.30.154 (talk) 21:07, 19 September 2008 (UTC)

RE: Citation needed, manual charging section: The potential for thermal run-away is the whole reason a charge controller is needed in the first place. As the battery begins to over-charge, the battery voltage drops. A "smart" charger is needed to notice this. If you are over-charging at a rate faster than the catalyst can absorb the Hydrogen and oxygen formed, bad things will happen: To quote my friend Kevin Schostek (e-mail correspondence (Tuesday, November 4, 2008)): ...I made a 32 AA-cell battery pack. It was built to have the individual cells removable, to be able to use just simple off the shelf NiMH cells. . . . Well, anyways, that battery pack was fine, but I never made a charger for it. (Like you mentioned, chargers of NiMH have to take into consideration temperature and voltage among other things.) I just charged it off my bench power supply, and sat nearby working on something else as it charged. I would monitor the voltage, and watch till the voltage peaked at around 50 V. Then it would be done charging, and would also be toasty warm.

So, I've been charging batteries like that for years. NiMH are the most difficult to charge "by hand," without a charge controller. But I still did it, even though I knew it was unsafe, and it was just a matter of time before I forget the batteries and severely overcharge them to the point of bursting them.

That time came on the afternoon of Oct 18. We had just finished celebrating my birthday, and I was distracted while charging my pack. I went out to help my brother fix his bike, figuring I'll be right back. I didn't come back for 15 minutes. And in total, the battery pack was overcharged for 10 minutes before my Dad threw the flaming tube out the front door.

My room stunk like burnt electronics for a week after that. I'm surprised they didn't kick me out altogether. The worst part is, it was my birthday, and it was a $200 battery pack that I spent a week making.

Looking for a page explaining why thermal run-away is a problem with Nickel based cells is like looking for a web-page explaining why bipedal walking is inherently unstable. It is something we all know and have to deal with.

Somewhat related pages:http://tlb.org/nimhboom.html Exploding NiMH Batteries

http://findarticles.com/p/articles/mi_m0PAE/is_2003_Summer/ai_109220052/ Thermal runaway

http://www.mpoweruk.com/thermal.htm Thermal Management 208.99.137.71 (talk) 06:06, 27 January 2010 (UTC)


 * Still another part of the article says it isn't a problem at C/10 or less. or use an alarm clock :) i'm more worried about my cheapo charger causing batteries to explode since they do run quite hot rather than having them explode while manual-charging 86.43.88.90 (talk) 21:16, 2 February 2010 (UTC)


 * It depends to a certain extent on the design of the cells. A catalyst such a platinum is needed to "burn" the Hydrogen and Oxygen formed at room temperature. The reaction is exothermic (though conceivably limited by the energy being added to the cell) so adequate cooling is needed to keep the temperature below ~45°C.


 * I have some Tenergy 10000 mAh NiMH cells. The rated trickle charge rate is only 800mA (2/25 C charge rate (0.08C)). For the C size 5000 mAh NiMH cells, the rated trickle charge rate is only 300mA (3/50 charge rate (0.06C)). They don't provide numbers for their smaller sizes.
 * Battery university seems to have relatively reliable information. 208.99.137.71 (talk) 23:39, 11 February 2010 (UTC)

Unsupported claims
Claims like these:


 * Still other actions by Cobasys suggest that the company remains unwilling to make NiMH battery technology economically feasible for the development of automobiles that rely on electric motor technology more than currently available hybrid cars.

...absolutely are not supported by the company's 10-Q financial filing which was used as a reference. Nowhere in the 10-q filing does that company reveal that it's trying to make electric cars economically unfeasible.

It's unlikely that any conspiracy by energy companies to bury the electric car would be announced in their 10-Q filings.

And this claim:


 *  including patents controlling the manufacturing of large nickel metal hydride batteries

...is not correct. Cobasys does not have a patent covering the manufacture of large NiMH batteries, but rather, it has patents on very specific improvements to NiMH batteries. Other companies manufacture NiMH batteries and have for decades. The text could be changed to reflect that; however it's questionable whether a patent on some very narrow improvement would be important enough to warrant inclusion in the article.

One more thing. Anyone could look at my editing history and determine right away that I am not a sockpuppet. I remind editors here to assume good faith, as per wikipedia policy.Twerges (talk) 23:30, 23 June 2008 (UTC)

...-I agree, this section is filled with hearsay that propagates the assumption that oil companies are universally evil companies trying to destroy our planet and force us into slavery ect.. ect...

It is perfectly normal for a company to not sell a product to the general public due to the minuscule profits in comparison to selling in mass quantities. Assuming that the company is making electric vehicles uncompetitive is intellectual dishonesty, at BEST. —Preceding unsigned comment added by 69.246.253.239 (talk) 19:20, 20 January 2009 (UTC)

Info box self-discharge of 30%
Shouldn't the self-discharge rate in the battery spec box be adjusted in response to the 'low-discharge' cells now getting mainstream? A figure reading 5-30% would sound better, considering the Sanyo eneloop's a value of less than 2%/month at 20 degrees Celsius on the long term. bkil (talk) 15:20, 12 August 2008 (UTC)


 * Those batteries have their own article. Link to it on this one somewhere Towel401 (talk) 16:44, 28 September 2008 (UTC)

Environmental impact
"Most industrial nickel is recycled, due to the relatively easy retrieval of the metal from scrap, and due to its high value."
 * This sentence should be removed from the article, or appropriately improved. In this context, it seems to be implying that the nickel in NiCd batteries (and NiMH batteries) is actually recycled.  In the US, at least, most consumer NiCd and NiMH batteries are trashed by consumers, and the nickel is not generally recovered.

-69.87.203.8 (talk) 23:21, 5 September 2008 (UTC)

internal resistance
What is the internal resistance of various types of batteries?

AA cells are the most comparable between technologies. Sanyo AA NiCd are rated at 16-19 milliohms (.016-.019 ohms).

There are 40 actual NiMH AA discharge data sets here. Looking at the middle of the 1 Amp and 2 Amp discharge curves, the difference is generally about .05 V (about 1.20 down to 1.15 volts); the lowest are about .03 V.  This implies that the effective total differential internal resistance of NiMH AA under load in the middle of discharge is about 50 milliohm (.05 ohm).

Sanyo Eneloop AA 2000 mAh LSD batteries have unusually high starting voltage under light load (.5 Amp), 1.48 V (compared to about 1.4 V for most NiMH AA batteries), and unusually high voltage under load, 1.25V at 1A and 1.21V at 2A, mid-discharge. So these would be particularly good for replacing alkaline AA batteries in equipment designed for alkaline. The RayOVac Hybrid AA 2100 mAh LSD batteries don't seem to have these unusual high voltages. What about other LSD NiMH batteries? -69.87.199.58 (talk) 15:40, 28 September 2008 (UTC)

Sanyo AA NiMH are rated at 25 milliohms (.025 ohms). -69.87.200.234 (talk) 01:56, 30 September 2008 (UTC)

Comparison of self-discharge rates of various types of cells
"The table below shows the approximate amount of time that it takes to lose 10% of the cell's current charge capacity at different temperatures.Clint Turner KA7OEI 20070105

These are typical values for new cells, published by various manufacturers. Note that aging/mistreated cells will probably exhibit much higher self-discharge rates."

We should have a table like this in each of the battery articles. -69.87.199.211 (talk) 12:22, 30 September 2008 (UTC)

Charge Cycle Life Data
batteryreview.co.uk has an educational set of 8 AA charge cycle data plots. They show that over 100 charge/discharge cycles, most NiMH batteries take a few cycles to get up to full capacity, and that some are able to keep full capacity for over 100 cycles. Some suddenly lose over half capacity, and then quickly regain full capacity. But two of the 8 start to lose capacity after 50 cycles, and another one loses almost all capacity after 50-90 cycles. It would be great to have a graphic like this in the article. -69.87.200.196 (talk) 14:02, 1 October 2008 (UTC)

Self-Discharge comparison
In 2007-2008, archae86 tested sets of LSD AA and AAA NiMH, and normal AA NiMH batteries. Self-discharge was measured for up to 3 months.

These are the capacity mAh data:

AA low self-discharge NiMH battery initial 1-hour 1-week 4-week 3-month 3m/1h% IME 1831 2186 2053 2008 1940 89% MAHA IMEDION 2100 mAh KPC 1723 2124 2021 1950 1874 88% Kodak Pre-Charged 2100 mAh GRY 1687 2116 1992 1938 1872 88% GP Recyko 2100 mAh DPC 1515 2010 1906 1857 1821 91% Duracell Precharged 2100 mAH HYB 1619 2026 1918 1870 1808 89% Hybrio by Ultralast 2100 mAh AMX 1645 2078 1936 1856 1784 86% Ansmann Max-e 2100 mAh ENO 1189 2017 1904 1854 1768 88% Nexcell EnergyON 2000 mAh ENL 1438 1980 1847 1811 1746 88% Eneloop by Sanyo 2000 mAh RHY 1738 2021 1867 1795 1716 85% Hybrid by Ray-O-Vac 2100 mAh RSK 1505 2024 1868 1808 1705 84% Radio Shack pre-charged 2000 mAHr ACC 1737 2022 1899 1790 1696 84% Acculoop 2100 mAh TPE 1009 1932 1847 1795 1590 82% Titanium Power Enduro 2100 mAh

AA ordinary NiMH battery initial 1-hour 1-week 4-week 3-month 3m/1h% PW20 * 1963 1804 1677 1259 64% Powerex 2000 mAh NiMH LC20 * 1727 1595 1498 1212 70% LaCrosse 2000 mAh NiMH KOD * 2072 1917 1673 1012 49% Kodak 2100 mAh NiMH SY23 * 2091 1899 1615 888 42% Sanyo 2300 mAh NiMH TI26 * 2001 1745 1495 781 39% Titanium 2600 mAh NiMH RAY * 1579 1471 1273  605 38% Ray-O-Vac 1600 mAh NiMH NEX * 1239 1211  978  533 43% NEXcell 2200 mAh NiMH TI24 * 2109 1859 836    0  0% Titanium 2400 mAh NiMH

AAA low self-discharge NiMH battery initial 1-hour 1-week 4-week 3-month 3m/1h% GR8 723 912 846 824 788 86% GP Recyko 800 mAh IM8 727 870 810 791 758 87% MAHA IMEDION 800 mAh EN8 600 838 783 765 734 88% Sanyo Eneloop 800 mAh DP8 622 833 780 757 734 88% Duracell Precharged 800 mAh AC8 543 779 724 697 632 81% Accupower Acculoop 800 mAh HY8 593 799 738 696 594 74% Hybrio by Ultralast 800 mAh

-500 hours capacity as delivered 0 hours zero-time capacity after at least three cycles 168 hours--one-week capacity 672 hours--four-week capacity 2184 hours--three-month capacity

Are there other sources of such self-discharge comparison data? It would be good to include such data and graphs in the NiMH articles. -69.87.204.244 (talk) 14:24, 2 October 2008 (UTC)

Power to weight??? -- All those references to power to weight, energy to weight etc are WRONG, WRONG, WRONG. These should refer to power to mass, energy to mass, not weight. Weight is a force. When you sling a battery into space its weight, and therefore its power to weight, changes. —Preceding unsigned comment added by 203.97.90.235 (talk) 23:24, 9 May 2009 (UTC)

Load and Current
Load is measured in Watts, current in Amperes, and current's symbol is I, not amps. Correct asap.79.49.182.225 (talk) 17:06, 7 September 2009 (UTC)

Move
consensus against move

Nickel-metal hydride battery → Nickel-metal hydride electrochemical cell — The electrochemical battery is simply a pair of electrochemical cells. this article deals around how this type of cell works.
 * Oppose. Electrochemical cell is not a synonym for battery. None of these many proposed renamings will improve the usability or accuracy of the encyclopedia. The present name is clear, accurate, and actually used in the world. Do not rename. --Wtshymanski (talk) 14:43, 9 October 2009 (UTC)
 * Strong Oppose and suggest speedy close (is that possible?). This is not what the general public would be looking for. HumphreyW (talk) 15:25, 9 October 2009 (UTC)
 * Opppose WP:COMMONNAME 76.66.197.30 (talk) 16:02, 9 October 2009 (UTC)
 * Oppose The term "battery" is almost always used by consumers, battery manufacturers, etc.  TJ   Spyke   17:30, 9 October 2009 (UTC)

Move discussion in process
There is a move discussion in progress on Talk:Lead-acid battery which affects this page. Please participate on that page and not in this talk page section. Thank you. —RFC bot 01:00, 11 October 2009 (UTC)

Naturalnews.com
I've removed the citation to naturalnews.com. This doesn't seem to meet the sourcing bar set forth by WP:RS, which asks that we use "reliable, third-party, published sources with a reputation for fact-checking and accuracy." I've tagged it for now; I will look for better sources. However, if the item can't be properly sourced, then it should be removed - that's a basic, basic application of the verifiability policy. Instead of restoring a poor-quality source, the energy might be better spent helping find a useful encyclopedic source. MastCell Talk 05:00, 18 December 2009 (UTC)


 * It looks to me like reputable news site; what's your beef with it? Dicklyon (talk) 08:21, 18 December 2009 (UTC)


 * I don't see many reputable news sites that publish a steady drumbeat of stories asserting that the pharmaceutical industry is intentionally poisoning and killing people for profit, or that the FDA is in the business of kidnapping alternative-medicine proponents who threaten the status quo, or that any celebrity who dies of a medical illness has been "killed by allopathic medicine", or the description of influenza vaccination as the "greatest quackery ever pushed in the history of medicine"... it just doesn't have that WP:RS ring to it. Why do you think it qualifies? MastCell Talk 19:26, 18 December 2009 (UTC)

Power density numbers are wrong
The tagbox says 300-1000 W·h/kg while the lead says it's 75. I believe the former is correct. Maury Markowitz (talk) 01:46, 8 April 2010 (UTC)


 * You are confusing power density and energy density. Article seems ok.Greglocock (talk) 04:34, 8 April 2010 (UTC)

writing and content problems
I started fixing the section on delta-T charge termination, then discovered the article has problems with writing (it's badly overwritten in places) and possibly misplaced content. I would rather discuss these with the original writer, before jumping in. WilliamSommerwerck (talk) 17:50, 19 September 2010 (UTC)
 * There are more than 500 contributors to this page, I suggest you go ahead and fix the style and rely on the Wiki feedback mechanism to tell you if you've gone too far. --Wtshymanski (talk) 13:22, 20 September 2010 (UTC)

Editing
As an example of how this article got into the mess stated above, please notice some anon IP desparately wants to add the following gibble-gabble to the article in the touching belief that it expresses the idea of cell reversal "more clearly": "This is because the current -shared and imposed by all the cells in series- creates a reverse voltage across each cell's internal resistance. This resistance increases as each cell is discharged, to the point that the reverse voltage at a discharged 'weak' cell can become greater than its forward voltage" As a general rule, if you have a large clause set off by hyphens, you're not writing very clearly. All the gibble about "internal resistance" is unecessary to explain that if one cell gets reversed, the battery gets hosed, which is the point. We don't need hundreds of extra null words to express the simple idea. --Wtshymanski (talk)
 * and the "citation" that is supporting this gibble is talking about ni-cad batteries, not ni-mh. The citation is a Web page that is a summary of a paper, and doesn't talk about "internal resistance", "current sharing" and the rest of the gabble. --Wtshymanski (talk) 17:06, 22 October 2010 (UTC)
 * Well, well, well. This  and this  say that one of the particular *advantages* of the nickel-metal hydride system is its ability to be reversed (at moderate currents) without damage. And this  does talk about the dangers of cell reversal but without respect to current level; it also mentions cell resistance is substantially constant during normal discharge, contradicting the gibble gabble. And this  says prolonged reversal will result in hydrogen evolution and perhaps venting.  --Wtshymanski (talk) 19:06, 22 October 2010 (UTC)
 * And now the offered citation "Solid state batteries" doesn't look any firmer, at least the bits I can see with Google Books. Pages 242-247 are part of a section called "Definition of full cell/battery parameters", and the accessible bits don't talk about cell reversal in general nor nickel-metal hydride batteries in particular.  And the other reference is still talking about nickel-cadmium battery cell reversal, again, not relevant to nickel-metal hydride. The phrase "current sharing" in connection with a series string is also just wrong, there's no choice about current "sharing" since it's a series circuit.  The proposed passage matches inaccuracy and obscurity with prolixity. --Wtshymanski (talk) 21:15, 1 November 2010 (UTC)
 * Gibble back in again, and none of the offered references support the "internal resistance" increasing. Wouldn't it be more sensible to quote some actual literature related to NiMh batteries instead of this highly original interpretation of two items that happen to mention "battery" ? --Wtshymanski (talk) 18:03, 2 November 2010 (UTC)

Patent encumbrance in electric vehicles
The article is worded in a way that implies that a single patent, granted in 1982, is still encumbering deployment of affordable NiMH batteries in electric vehicles today. That cannot be the case, because any patent granted in 1982 would have expired in the USA by 2002. If, today, there are still patents in effect which would encumber the deployment of affordable NiMH batteries in electric vehicles, then those patents must necessarily be newer than the 1982 date mentioned in this article. And if that is the case, then what are those additional patents? 24.222.2.222 (talk) 12:16, 18 February 2011 (UTC)

Removed memory effect section
The sole source (web page) for the section saying that NiMH's suffer from a memory effect no longer exists. I tried to find its new location on the same site, and actually discovered that the site suggests that NiMH's *don't* suffer from memory issues:


 * "A properly designed application with Ni-MH batteries will result in neither permanent performance loss nor perceivable temporary capacity decreases from this characteristic." Duracell

All other sources I found also said that NiMH's don't suffer from memory effects. MichaelBluejay (talk) 16:29, 12 May 2010 (UTC)

Linden and Reddy's Handbook of Batteries, 3e (2002), discusses the "Voltage Depression (Memory Effect)" in section 29.4.9.
 * "A reversible drop in voltage and loss of capacity may occur when a sealed nickel-metal hydride battery is partially discharged and recharged repetitively without the benefit of a full discharge."

The explanation given is that only a portion of the active materials are cycled, and the uncycled portion "change in physical characteristics and increase in resistance." This is consistent with the explanation by Sato, Takeuchi and Kobayakawa, Journal of Power Sources, 93 (2001) 20-24, where the authors report that a small portion of the positive electrode active material is converted to gamma-NiOOH in a reversible manner. Data from Duracell is also provided in Linden to show the effect and that it is largely or fully reversible (figure 29.13). Note that the Duracell site is talking about "properly designed application;" not "properly designed battery" or "technology." In my experience, the NiMH industry has attempted to distance itself from association with the better-known and more damaging memory effect found in NiCd. Tom Hopper (talk) 10:11, 3 March 2011 (UTC)

Amperage limited charging method using solar cells
I do not have the manuals from which I learned the amperage limited charging method. In this method, the charging rate is amperage limited, rather than limiting the voltage. A voltage at around 150% of the voltage of the battery (or series of batteries) is applied in reverse. The exact voltage is of small importance as long as it is not too high. The amperage must be limited to one tenth the capacity (denoted C/10) or less. NiMH batteries are designed to accept up to a C/10 level of amperage for charging. More than C/10 will cause hydrolysis of the electrolyte solution (which is KOH in water). This method is ideal for charging directly from solar cell panels, as solar cells are amperage limited in their output. Ordinary solar panels designed for 12 volt systems (output ~15 to ~20 volts) can be used to charge 12 volts series NiMH batteries as long as the current produced by the panel does not exceed C/10 of the battery. A 6 volt solar panel (output ~7 to ~10 volts) can be used to charge series connected NiMH meant for 6 volt electronics. As an example a AA NiMH battery rated at 2500 milliamp hours can be charged at an amperage of up to ~240 milliamps. A series of 2500 milliamp hour batteries uses 250 milliamps as well. With charging in parallel, such as four of these 2500 milliamp hour batteries in parallel, a charge of up to <10 amps may be applied. I used this method to charge batteries to run a short wave radio and a night lamp. It works well. My Flatley (talk) 00:42, 25 September 2011 (UTC)

Storage
What are optimum long-term static storage conditions for NiMH batteries? Not to maintain immediately available charge, but to minimize permanent capacity loss? Some sources say to store at about half charged, other sources say that for Ni chemistries charge state is not important. Cool temperatures seem desireable, but better not to freeze? If storing for years, would it be better to trickle charge at a very low level, to avoid full discharge? (batteryuniversity.com/learn/article/how_to_store_batteries) Different manufacturers seem to say rather different things: (www.powerstream.com/Storage.htm) There is general agreement that charging behavior after storage may be unusual the first cycle, and capacity may be regained over a few charge-discharge cycles. -96.237.13.111 (talk) 04:44, 27 November 2011 (UTC)

Claimed voltage of charged cell
Article has an unsourced claim that the open circuit voltage can be 1.4 volts and even as high as 1.5 volts. Real world batteries are unaware of this. Indeed the electronegativity of the materials used to construct NiMH batteries is such the highest possible E.M.F. is 1.37 volts. 86.176.69.42 (talk) 16:40, 17 January 2011 (UTC)


 * Verbrugge and Tate provide graphs showing OCV of just below 1.35 V one hour after end of discharge @ 90% SOC and just below 1.45 V one hour after end of charge @ 90% SOC. OCV values are shown ranging between about 1.22 V and 1.45 V depending on SOC and whether the previous step in testing was discharge or charge. See Figure 3 of Verbrugge and Tate, Adaptive state of charge algorithm for nickel metal hydride batteries including hysteresis phenomenon, Journal of Power Sources 126 (2004) 236 - 249.
 * Linden and Redy's Handbook of Batteries, 3e (2002), provides data from GP Batteries showing discharge voltage at the start of discharge ranging between 1.4 and 1.45 V (figure 29.4 and 29.5). Personally, I believe that this is a residual effect from charge (i.e. no pause between end of charge and start of discharge), but in any case it also fails to contradict the claim for high OCV. Tom Hopper (talk) 10:35, 3 March 2011 (UTC)

This 1.37 OCV max theory seems very at odds with real reality. A set of 2006 eneloop NiMH AA batteries has been recharged a few times yearly since 2007. The max voltage in the charger reads over 1.5 V. The OCV right after removing from the charger is about 1.48 V. The OCV after resting about half a day is about 1.42 V.-96.237.13.111 (talk) 17:49, 27 November 2011 (UTC)

Reference 14 unavailable, found alternate URL
The Duracell NiMH handbook is no longer available on the Duracell web site. A Google search brought up a copy at an alternative source. I edit the URL in the article and add this comment in case this alternate URL might consiture a copyright infringement. Jlbruyelle (talk) 21:58, 28 July 2012 (UTC)

Wasn't Thomas Edison The Real Inventor?
The history says "The earliest pioneering work on NiMH batteries ... was performed at the Battelle-Geneva Research Center starting after its invention in 1967." But Thomas Edison was the true inventor of this type of battery.

Edison had numerous patents on it, for example February 4, 1908 896,812 Storage Batteries. His focus was on large scale batteries to replace lead-acid, but still, the technology was his. See the book "Edison His Life and Inventions" by Dyer and Lewis Chapter XXII. — Preceding unsigned comment added by Anorlunda (talk • contribs) 20:53, 14 April 2012 (UTC)


 * No he wasn't. Edison patented a few types of rechargeable batteries based on Alkaline technology (all derived from the Nickel-Cadmium technology) in 1901.. However, Edisons work, like most of his inventions, was stolen.  Valdemar Jungner patented the Nickel-cadmium battery in 1899 and had experimented with all Edison's materials as an alternative to cadmium (principally to reduce the cost).  Edison's principal contender, the Nickel-Iron battery was experimented with by Jungen and rejected as inferior to the Nickel-Cadmium. 86.144.90.137 (talk) 14:53, 9 September 2012 (UTC)

List of "Low self-discharge cells"
How about making a list of all low self-discharge cells that we know of? I believe that would be useful to people, especially because for most uses they have clear advantage over regular NiMH cells (for most purposes people don't drain batteries at once). I actually see no purpose of using regular NiMH cells other than initial higher capacity after recharging (and how long does it actually stay higher? Does The self-discharge is 5 – 20% on the first day and stabilizes around 0.5 – 4% per day at room temperature apply to LSD cells also, or only to regular NiMH cells?). ...
 * Eneloop
 * Eneloop XX
 * Varta Longlife Accu Ready 2 Use
 * Varta Power Accu Ready 2 Use
 * Camelion AlwaysReady
 * Duracell StayCharged

Maybe even putting them into a table, putting pictures, listing declared capacities? Marekich (talk) 15:22, 9 December 2012 (UTC)

High voltage
What happens if I charge NiMH batteries with higher voltage. Or the voltage for AAA/AA batteries is a standart? Only the mA charging rate is different? —Preceding unsigned comment added by Leonardo Da Vinci (talk • contribs) 11:21, 21 May 2010 (UTC)


 * In general, nicad and NiMH batteries should be charged constant-current -- or something approximating it -- not constant-voltage. WilliamSommerwerck (talk) 23:46, 10 November 2011 (UTC)


 * Not 'in general' at all. Ni-MH (and indeed Ni-Cd) batteries should never be charged in a constant voltage mode.  Both exhibit a negative temperature coefficient characteristic (with it being more much greater in the Ni-MH due to its exothermic charge reaction).  This means that as the battery warms during charge, it's internal resistance drops, the charge current rises, the cell warms more, the internal resistance drops more, the current rises more ... and thermal runaway results ending in a spectacular destruction of the battery.  I B Wright (talk) 18:16, 17 December 2013 (UTC)