[zackees]

Also, NiMH batteries can reverse charge and ruin themselves. This happens a lot when batteries are in series and the load will continue to run the batteries until 0 voltage. The weakest battery will deplete first but then the other batteries will continue to pump current through until that weak battery reverses polarity and wrecks itself.

[hilbert42]

Correct, ages ago, I was testing a batch of them and came across several reversed charged ones. At first I thought I must have got my multimeter leads reversed but I found that was not the case.

For a long while I kept them to prove the point to anyone who thought I'd must have lost my ability to distinguish plus from minus.