I thing the issue is that the Novak HV gets the current for the BEC from ONLY one of the connectors (I think is the right one).

If you use 6 or 7 NiMH cells packs the BEC works reducing 7,2 or 8,4V to 6V for the receiver and servos.

Using a 12V lead battery or 4S lipos in this connector will overload the BEC and can burn it.