you can get away with three cells. The parts on the PCB are rated @ 5 volts, and 3 cells is only 1.2+1.2+1.2=3.6. If u really want to go fast(and I mean
FAST) you could do a quad cell. The two motors will work also, it won't provide more speed, but it will give lots of torque. The only thing you might worry about is how you mount it. Use epoxy, but be careful of the axle and the gears(it's happened, not fun!!). Super glue just doesn't cut it here.......Anyways, have fun!!!!!
