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How to recharge completely dead NiMh

workthelights 217 36 November 7, 2010 at 11:04 AM
A few years ago I bought 4 Kodak NiMH AAs and 4 AAAs with a charger. I was moving about that time and everything got boxed up and forgotten about. Now I have dead batteries and the charger won't charge them. What should I do? Should I properly dispose of the batteries? Buy a better charger--which one?

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#2
Try charging each cell individually until the voltage exceeds 1.0V. Most chargers can't do one cell at a time, but some trickle chargers that require 12-24 hours for full charge can, at least if you put in just one cell and then short each unused space. Don't leave the cell in there for more than 1-2 hours if you do that because the current will be higher than trickle charge level. Also don't try this with "hot" chargers that require a plastic cover be closed before they'll turn on (no transformer isolation, can be a shock hazard if run while open; Radio Shack used to sell them).
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#3
If you're looking for a charger...

http://www.amazon.com/Crosse-Tech...787&sr=8-7

You could get the higher end version too but the 700 was able to resurrect old dead batteries for me.
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#4
What are you going use the Kokak NiMH for?

For cameras and most uses, regular NiMH discharge so much after 2 week that they become useless and are a hassle to recharge.

You might want get Low-Discharge (LSD) Batteries like Sanyo Eneloop / Rayovac Pre-Charge.
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#5
Quote from FAL View Post :
What are you going use the Kokak NiMH for?

For cameras and most uses, regular NiMH discharge so much after 2 week that they become useless and are a hassle to recharge.

You might want get Low-Discharge (LSD) Batteries like Sanyo Eneloop / Rayovac Pre-Charge.
Hmm, I didn't know about the short life. I wasn't planning on using them in my camera, they just happened to be Kodak brand. Just wanted something for kids' toys.
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#6
Quote from workthelights View Post :
Hmm, I didn't know about the short life. I wasn't planning on using them in my camera, they just happened to be Kodak brand. Just wanted something for kids' toys.
they'll work fine. but you'll probably have to charge them before you use them each time.

Not very useful for emergency purposes, but work fine if you are expecting to use them, and have time to charge.
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#7
Quote from workthelights View Post :
Hmm, I didn't know about the short life. I wasn't planning on using them in my camera, they just happened to be Kodak brand. Just wanted something for kids' toys.
As fyu said, your current batteries will work fine. Just keep them in the charger until you're ready to use them. For toys that draw very little power but still need batteries (things with remote controls, IR laser tag guns, etc.), I would suggest either investing in low self-discharge batteries like Eneloops or buying alkalines. Alkalines are fine for uses like that because they last a good long while and don't self-discharge.

Back to your original question, there are two things that could be wrong. One, more likely, is that your charger could be broken. You could just try borrowing a charger from a friend and using that one to see if your own charger or the batteries are at fault. If the batteries are dead, a smart charger may be able to revive them. Look into the Ansmann Energy 8, the Maha PowerEx MH-C9000 WizardOne, the La Cross BC-700, and the La Cross BC-9009. All are excellent units capable of reviving most dead batteries. Of them, the BC-700 is the least expensive and will probably do everything you need it to do and more.
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#8
If you need a new charger.

I go with Sony or Sanyo. Sanyo makes hi-quality battery that sony also use. I am using mind 5 years strong. The one I purchased has an extension cord rather that just wall plug.


Charger:
http://www.amazon.com/Sanyo-Enelo...67&sr=8-17 (Sanyo Single Kit)
http://www.amazon.com/Sanyo-27726...01&sr=8-10 (Sanyo Power Pack)

Batteries:
http://www.amazon.com/s/ref=nb_sb...yo+eneloop
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Last edited by atrix415 November 9, 2010 at 07:14 PM
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#9
Quote from Mixels View Post :
As fyu said, your current batteries will work fine. Just keep them in the charger until you're ready to use them.
Don't keep them in the charger because that will cause dendrite shorts to grow inside them, even if the charger is the smart type. Nicad and NiMH cells do discharge relatively quickly in storage, but they don't drop that much in just two weeks, and there are low-discharge NiMHs from Sanyo, Sony, Panasonic, Rayovac, and Kodak that maintain almost full charge even after 8-12 months, some labelled "pre-charged".

Dumb chargers are sometimes better at reviving completely dead cells than smart chargers are because the latter often run a test of the cells at the beginning and refuse to charge if they sense problems. This is done to protect against things like charging cells that can be dangerous to charge (alkaline, lithium) or shorted cells.
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Last edited by larrymoencurly November 10, 2010 at 01:11 AM
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Quote from larrymoencurly View Post :
Don't keep them in the charger because that will cause dendrite shorts to grow inside them, even if the charger is the smart type. Nicad and NiMH cells do discharge relatively quickly in storage, but they don't drop that much in just two weeks, and there are low-discharge NiMHs from Sanyo, Sony, Panasonic, Rayovac, and Kodak that maintain almost full charge even after 8-12 months, some labelled "pre-charged".

Dumb chargers are sometimes better at reviving completely dead cells than smart chargers are because the latter often run a test of the cells at the beginning and refuse to charge if they sense problems. This is done to protect against things like charging cells that can be dangerous to charge (alkaline, lithium) or shorted cells.
NiCd batteries have that problem. NiMH batteries don't. It is A-OK to keep NiMH batteries on a smart charger. Leaving them on some super old and low quality dumb chargers, however, can cause overcharging, which is bad. Any charger purchased in the last five years or so should be fine.

About your second part: the process of reviving dead batteries involves fully discharging them and then recharging them several times. Dumb chargers are not capable of doing that. At all.
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#11
Quote from neteng101 View Post :
If you're looking for a charger...

http://www.amazon.com/Crosse-Tech...787&sr=8-7

You could get the higher end version too but the 700 was able to resurrect old dead batteries for me.
Iagree I have that one and it's "fixed" batteries that my dumb chargers couldn't make work.
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#12
Quote from workthelights View Post :
Hmm, I didn't know about the short life. I wasn't planning on using them in my camera, they just happened to be Kodak brand. Just wanted something for kids' toys.
If you live near a Walmart/Target, for under 15.00 you can get a new "dumb" AA charger with a fixed timer. For camera use, buy any replaceable battery with the words "PRE-charge" on it.

For kids toys, get 12 AA Rayovacs for 5.00 at Walmart or COSTCO
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#13
Quote from larrymoencurly :
Don't keep them in the charger because that will cause dendrite shorts to grow inside them, even if the charger is the smart type.
Quote from Mixels View Post :
NiCd batteries have that problem. NiMH batteries don't. It is A-OK to keep NiMH batteries on a smart charger
Dendrites are a problem with nicads, NiMHs, and even lead-acid batteries, and they weren't, then why have makers of NiMHs boasted of their plate separators being more resistant to dendrite piercing?

I don't know where you got your information about fully discharging dead cells because they shouldn't be allowed to go below about 1.1V or else they'll be damaged permanently. The applications notes for Maxim and Linear charger chips mention this.

I used to think smart chargers would turn off enough at full charge to prevent damage, but apparently they don't, and people who keep their tool nicad and NiMH battery packs plugged into their smart chargers with full charge, top-off charge, equalizing charge, and maintainance charge modes that pulse to break down dendrites don't usually get as much life as people who remove them.
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