I have had problems with this also on the kero start with duralite batteries. So I switched to the Fromeco peerless series witch can handle a 13 amp continous discharge and they are 4800 mah. Duralite can handle I belive it is 6 or 7 amps continous.
I do know that we have a local guy flying with a 2s2p [4200mah] that I sold him for his kero start that also works fine.