You probably want a name-brand high capacity NI-MH rechargeable.

The higher capacity the better and to improve their lifespan use a "peak-detecting" charger, specifically one that is designed for the new NIMH cells. Newer chanrgers will avoid over-charging the batteries, which will decrease their lifespan.

The higher the mAh number the better, which makes sense... more power means it will last longer.

You probably want a name-brand high capacity NI-MH rechargeable.

The higher capacity the better and to improve their lifespan use a "peak-detecting" charger, that will avoid damaging the batteries.

The higher the mAh number the better.

There is a good review of the top brands at www.metaefficient.com