Heli guys do this all the time, its a common question - like I said IIRC (and I didn't...) the batts are wired together in series (2 3S in this case to make a full 6S) and the balance wiring is also serialed (not paralleled!!!), this converts 2 3S lipos into a 6S1P. You have to have the balance taps serialed otherwise balancer can't see each cell.

http://www.rbgrn.net/content/46-how-...ks-single-6s1p