RE: Ofna starter box battery upgrade?
Yes, 3S will work... I have one in my dynamite starter box which uses one of the larger high torque motor and lets me start my .21 engine very well. The 2s however lacks the muscle...
but, If you'll be using high compression engines better be safe and get a 4s... if you have a buddy that has 3s talk him into letting you try it, it will only take a few seconds to find out if it has the juice to start your motor.
MAke sure you get a lipo with high mah preferably : 5,000mah or higher so you don't have to recharge too often.
and if possible, get a lipo cutoff, or just watch the voltages with a voltmeter every now and then , remember 3.2 volts per cell minimum, that's 9.6 volts or higher on the 3s pack and you're ok. hit 9volts and you're still safe but you'll have to charge it.