I had some NiMH Ansmann AA batteries in a drawer for a while (2 years+) and when I went to charge them I noticed that about 20% of them were giving some kind of error on the charger (if they charged at all that is). I started charging and checking each one using a multimeter. Some were completely dead. The best ones were putting out 1.3+ Volts. Some were in the 1.1-1.2 range, which probably is still acceptable for some applications.
Given that I had not used these batteries hardly at all when they were brand new, I was confused that so many were bad and also wondered at the varying outputs of those which were still “good”. I remember reading up on the care/use of rechargeables when I first purchased the batteries, but I guess somewhere along the way I forgot what I learned.
Anyway, here are some basic guidelines for NiCd / NiMH batteries for those who are curious. I pulled this info from:
Best way to charge:
Avoid getting battery too hot on charge.
Do not leave battery in charger for more than a few days.
Subject to memory.
Constant current, trickle charge at 0.05C, fast charge preferred.
Slow charge = 14h
Rapid charge = 3h
Fast charge = 1h
Do not over-discharge on a heavy load; cell reversal causes short.
Avoid full discharges
How to prolong battery:
To prevent memory, discharge packs in regular use to 1V/cell every 1–3 months (mainly NiCd)
Store in cool place; NiCd stores for 5 years; prime before use
NiCd: Do not dispose.
NiMH: May be disposed in low volume
Upon reviewing the above, I can see why my batteries no longer perform as advertised. Some were getting too hot on charge. Some were left in the charger for more than a few days. When I had them in my external camera flash they were probably getting over-discharged on a heavy load. That same flash may have also caused cell reversal because I stored some batteries under load inside the flash until they discharged. What’s also interesting to note is at this point none of the batteries (even those putting out the most juice) will power my external flash. I’m not sure if that’s due to a reduction in output because of their age, internal damage, or some damage to the flash itself but I had to buy some regular AAs to get my flash going again. Maybe I will buy a pack of 4 brand new rechargeables to compare to my old ones so I can determine the real reason my flash won’t fire…if so I will update this article.
Until then, good luck and don’t forget to be kind to your rechargeables.