As far as AA cells go, about the highest accurate stated energy rating for rechargeables is 2500 mAh rating (Quality cells - anything go for cheapies).

"Battery chargers" for modern advanced rechargeable cells are no longer 'cheap and nasty', they can be internally quite complex, even using PICs (programmable ICs - like tiny computers) to give multiple rates/levels of charging current, depending on the initial battery state at start of charge, and even a 'holding' charge - the good ones also cannot overcharge and damage the cells either.

A good investment if you want to use the cells a lot for best economy.

Note that most rechargeables will lose a % of charge all the time till totally discharged - the LiMH ones lose a much lower percentage. You cannot store charged rechargeables for months and then expect them to be holding a full charge.