get a lipo battery, a 3 cell 11.1v 4000mah will do the job...this is what i'm using, no problem starting a .21, .45, .67 OB/IB motor...also, it doesn't need a regular charging, it last long,,,,,hobbyking sell pretty cheap lipo.
if you want more cranking 6 cell lipo 22.2v but this is to...