We have our eyes on 5Ah ones as it allows for a relatively high discharge, and long playtime. Tormenta 2 currently runs very nicely on about 65a overall discharge available from its NiMH packs. We will be upgrading to a LiPo that can supply at least 100a. Not massively powerful, but the likelihood of all 5 motors stalling is tiny, and we'll run a fuse just in case.