You really don't want to push your batteries too hard. Fast charging will shorten their life as well as increase the risk of them overheating and setting your house on fire. The same goes for over stressing them by pulling too much amperage by over propping the motor. Hot batteries are like hand grenades just waiting to detonate.
Also this question would have better response in the electrics forum. This one is about internal combustion engines. Just sayin'....