A quick note on NiMH batteries, specifically the low discharge ones. If you buy a package and they are labeled ready to use, that means they are low discharge.

Sometimes I find that when I put a dead battery in a charger, it does not seem to charge to full capacity. Example, yesterday my living room wall clock with a NiMH AA quit running, so I swapped batteries. Put the dead one in the charger. The charger should have put over 2000 mAh into the battery, but only put in a bit over 1000mAh when it said it was full this morning Thus, not fully charged. I use a charger (Accupower IQ-328 that I think is over a decade old) that can also discharge and recharge batteries, it also does that on each cell individually. This morning I set the charger to fully discharge that battery and recharge it, I was impatient so I set it at a higher discharge and recharge rate. Just checked it now, it is done charging, this time it put in 2420 mAh into the battery. That is close to the battery rating.

I have often found that if I discharge a battery to really low voltage, example less than 0.75v, it only takes a small bit of charge the first time I charge it, it needs a few discharge and recharge cycles to get it back to working up to full capacity.

Also, if you are unhappy with the NiMH batteries you are using, if the charger needs to have two batteries in it to charge by charging them in series. In that case if a battery is half empty and the other empty, the same number of electrons go through both batteries when charging, thus it will not fully charge the fully discharged one. I have a couple older chargers that only charge pairs of batteries that way.