What kind of capacity should the AA cells have?

Currently, the total capacity of the battery is 3500mAh, so if the AAs were to match that one, and I used 8, they would need to be about 450mAh each.

However, most of the AAs and AAAs in the catalogue are rated at around 1500mAh.

I'm guessing we don't want too much capacity. Anyone got any suggestions as to what would be ideal?