a very good battery pack is the Sanyo Eneloops [ 5 cells ] 6 volts no reg needed. if you want to use a lipo pack go for 2500 mah / 2 cell which is 7.4 volts and abit higher when freshly charged . you will need a regulator for this so have a look at Big Bruce Racing at his regulator at around $20. very light and works great.