Full charge detection with older NiMH cells

[Circlotron]

I have two sets of four size AA nickel metal hydride cells that are used for my radio. Once set is about three years old, and the other one is only maybe three months old. With the older set, sometimes one or two of the the cells when on charge instead of cutting off at about 2800 mAh will go all the way to 4000 or so. Does this mean they are getting towards the end of life and the decrease in charge voltage at full charge is getting less well-defined?

[Gyro]

Possibly an increase in internal resistance that, yes, makes the charge voltage drop (more shallow with NiMH, than NiCd to start with) less well defined. That's only a guess though.

To keep them out of e-waste, as long as you're charging when you're around, do a periodic finger test - when they get significantly warm, they're done. It's the end of charge temperature rise that causes the voltage droop.