I had taken on the task of going through my dozens of AAs and weeding out the duds (some are over seven years old).
Well.........turns out over 80% seemed useless.....won't charge or would only take a half-assed charge.
Instead of tossing them I studied a while on how to possibly rejuvenate them through a series of controlled charge/discharge cycles.
This was too hard to do with my inexpensive charger, so I bought a MAHA MH-C9000 charger ($50), which has a couple features that will fix old batteries.
After about thirty hours, my first set of "duds" seems to be satisfactorily refurbished.
Just thought I'd let y'all know.....this is a really cool charger, complete with a readout that allows you to monitor and evaluate batteries individually.