If you want my advice (which you most probably didnt, but meh), you could probably get away with two NiCad packs in a robot with two wheels driven by two motors that isnt a pure pusher, like a thwacker or similar. Things like having four wheel drive, tracks, more motors, electric weapons, and the like will increase the amount of power you need, up to say four packs for a four wheel drive robot with a weapon, possibly six if you have a lot of motors or a big current-heavy spinner (in which case go petrol :P) I wouldnt bother with stating capacities and discharge currents unless you really feel the need to, since its just not important to battle writers.

NiCad packs should be fine for just about any robot - selaed lead acid are a touch on the heavy side, and with NiMh, A123, Li-poly, and other technologies, you have to know what youre talking about to be able to use them, and the weight saving is negligible.