they have all kinds of lipo batteries....i dont like them i use trinity 3800mah batteries 6 cell with a 19t motor and it have ALOT of power left even from a 5-7 minute main so a 4200mah batterie with a checkpoint 10 double would be fine.... nimh's are cheaper than lipos and nimh's can be used on any charger and discharge after race day with lipo no all chargers support them they have to be balanced you really dont know when theyre fully charged or going to die and when lipos die they really do....theres a slim chance to bring them back but they have equipment to simplify this like novak they have a lipo stop so you dont damage your $100+ lipos and a intellepeak ice charger has a balancer built in it so you can balance your pack while you charge so they're both good it just depends on what you want and run and how deep your wallet is thats about as easy as it gets