I can remember when a battery used to hold its charge for weeks or months. With some of the NiMH's now it seems like they are down 50% in a few days just sitting on the shelf.
Yes, these are brand new. Probably Chinese. Does it have to do with inferior materials, or what?
Is there anyway to get them to hold a charge longer? Someone suggested wiring an alkaline battery of similar voltage in parallel. Not sure about that.
Put it in the freezer?
Any suggestions?
I don't believe it is a problem with the charger, since the same thing happens across a few devices.
Bad idea - the alkaline is 1.5 volt the NiMH is less (a little variable depending on state of charge). If the NiMH went flat in a couple of days so will the alkaline if connected to the NiMH - and didn't you want NiMH to save on batteries.
You could build a custom charge to "float" charge the NiMH. They don't like it very much and you should find a way to "pulse" the charge so it only intermittently charges the batteries.
That's called "self-discharge" (discharging all by itself, on the shelf).
There are a number of low self-discharge NiMH for sale, including Eneloop, certain Energizers, and RayOVac. I like the RayOVac.
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RayOVac used to call their low-self discharge NiMH "Hybrid" and Energizer called theirs "Precharged," but they keep changing the names. Look on the back for the ones that say they hold a charge for half a year (or more).
Sometimes the answer is really simple. This stuff sucks...OK, buy something that doesn't suck.
Doctor, it hurts when I do this. Well stop doing that!
My understanding is depending on where you live, Eneloops are kind of expensive. Or they rip you off on the charger. But in the US and with deals from Costco, why use anything else.
I think you are right that capacity is about 25% less than state of the art, but with low self discharge, you generally come out ahead.
** Have to consider those to be faulty cells.
** Probably all three.
** Mad idea.
Rechargeable cells are best in *high drain* devices that are in regular use, alkalines are better for occasionally used items - like that torch you keep handy for emergencies.
Digital cameras are a particular problem - you may use them infrequently but many draw so much current they do not perform well on alkalines.
One option is to leave your NiMHs on permanent trickle charge until you need them - about 50mA for 2000mAh AA cells.
Are you sure they are actually the capacity they say even originally ? There are many cheap Chinese batteries branded as "2700" or even "3000" mAh capacity. Have had several, and measured capacity is more like
700-900 mAh for all of them, even after several charge-discharge cycles. Never really measured the self-discharge rate, just threw then in the "duds" bin.
Eneloop or equivalent is the best, as already said.
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Regards,
Adrian Jansen adrianjansen at internode dot on dot net
Note reply address is invalid, convert address above to machine form.
Keeping the cells cooler might slow down the self-discharge rate, but I don't think freezing them is a good idea. I will cheerfully admit I have no evidence one way or the other.
Sanyo Eneloop cells. I bought a set of 8 in 2011 and they do what they say on the tin. I use them two at a time in my Nikon point-and-shoot digital camera, and they work great, on three continents so far. I got mine from Amazon.
For the first couple of years, I charged them in a Rayovac PS12 smart charger (home or road). Now I use a spiffy Maha/Powerex MH-C9000 smart charger, at least at home. The spiffy charger shows me that they lose much less capacity when sitting, compared to the older NiMH cells I own (China Rayovac and Singapore Radio Shack).
There are apparently some subtle design changes over time in the Eneloops, and some people prefer one version over another. Mine are "HR-3UTG, typical 2,000 mAh, minimum 1,900 mAh" and made in Japan.
Sometimes the Eneloops are available in a bundle with a charger, but Google it first; I have seen bad reviews of the bundled chargers before.
Also, don't buy cells with no capacity markings, no matter the brand. I got the Chinese Rayovacs 6 or 7 years ago at what would have been a great price for 1,800 or 2,000 mAh cells. In use they subjectively didn't do quite as well as the (much older) 1,500 mAh Radio Shack cells. Once I got the Maha charger, I ran a few "analyze" cycles on them and found out they were 1,300 or 1,400 mAh at best.
If you like gadgets, get a charger like the Maha that will display how many mAh it has managed to put into the cells. It also has a discharge mode, automatic discharge/charge and capacity reporting, and other fun stuff.
With any charger, get in the habit of recharging your spare rechargeable batteries at least once every month or two. Do it at the first of the month, or on the day of your birthday in even months, or whatever helps you remember. This goes for the NiMH cells in your digital camera, the NiCd or Li-ion batteries for your power tools, the NiMH batteries in your laptop, the PbA battery in your riding lawnmower or old car, whatever.
Also, like Phil said, NiMHs are not for everything. If the device sits for a long time between uses, or has really low current requirements, plain old alkalines might serve better.
I have Tenergy Centuras in my digital camera. With infrequent use, it goes for months between charges. I think these are a substitute Eneloop, but they seem to work just fine in any case.
The problem lies in mfrs making the electrode separators too ultra-thin to cram in more capacity. The cure is in an improved separator, not the refrigerator.
Seems like reasonable advice to me. He may just have got a bad batch or is storing them at an elevated temperature or using them in an unsuitable device. Low self discharge NiMH are greatly superior at holding charge to the ordinary run of the mill ones which lose around
1-2% per day. Perhaps even worse if they have been seriously abused.
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The other factor is if you use them in sets of four then likely one cell will be weaker than the others and fail prematurely. The set then stops working when the weakest link fails. Weeding out defective cells with a simple battery tester will help avoid this mode of failure.
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