I think I know the answer already, which is to chuck it. I have several old energizer and Duracell AA nimh batteries. By older, I am thinking 6 or more years old, and sitting in a drawer. I did not expect much out of them. I charged them all (at least the ones I could) with my 15 minute energizer charger. Then I started charging them one by one with my old RC battery charger, a Piranha digital peak charger. Then discharge them in a battery at about C/5 rate, and charge at C/10 rate. I have several that are holding at least 2000mA hours now. But one is measuring open circuit at around a volt. I am thinking it is done for, but is this recoverable?
Yea its fine. They may take time to recover the lost voltage but they will gain capacity with the more charge and discharges you do.
The one that is broken i am not sure about is there ant residue around the terminals? What about if you trickle charge it to raise the voltage really low? like 50ma or 100ma?
The open circuit voltage is about 1.0 V, and there is no residue or funny stuff on the one anywhere. Other ones that are discharged presently and awaiting their turn on the charger are between 1.1V and 1.25V. The 1.25s are 1300mAhr Rayovac cells that I thought were pretty discharged but seem to be fine now . . :question:
I think the lowest current on my charger is 0.1A, so that is the slowest trickle I have handy. I have a power supply that I could use and adjust trickle current lower.
Are they LSD NiMH? At worse the batteries will just overheat there isn’t to much danger in trying to charge them. 1v is still fine my NiMH usually charge up to about 1.5 volts. resting voltage is usually about 1.37 volts some where around there. Some brands may be 1.3 other 1.4 resting.
I think a lot of the capacity of a NiMH is between 1v-1.3v. They can discharged down to 0.8v so 1v is fine overall.
I find when they won’t hold a charge for a few weeks they are toast. I used to have some energizers that were dead in a day, hard to work a photography gig with batteries like that.
Which is the safest way to really fry older cells. These chargers are mean enough to even make toast from good ol’ eneloops, if used regularly. Usually ~1C is the maximum current for charging nimh cells without permanently damaging cells. Using 4C as in 15 minutes will kill them in no time. Once had a charger like that, but after killing a second set of cells in ~5 charge cycles it went to where it belonged to: Recycling yard.