[lincpimp]

Watts divided by volts will give you amps. conversely amps times volts gives you watts. You also have to figure that the system will only be around 70% efficient, so your batt needs to be that much more capable.

Say you have a motor that can pull 2000 watts. On 6s lipo your batt would need to be capable of 90amps - 2000/22.2=90

But you have the efficiency to think about, so 90/.70 = 128, so you would need a batt that could deliver aroound 128 amps cont, and not drop the voltage below 3.7v per cell. Most lipos do experience voltage drop nearer 3.2v per cell and heavy load.

So something in the neighborhood of 150 amps cont will cover voltage drop, efficiency losses, and poor math...

Always good to state your lipo choice too, as many packs are rated much higher than they can deliver, and the only way to know that is thru experience...