[ebarker]

NO !!
The nicad battery pack has to be the same pack in the kit, or another of the same part number. Building a larger pack increases the amount of stored energy and is disallowed.

The correct was is to build the IFI charger circuit.

we built a circuit last year that was similiar that provided a 6 volt bus that was regulated down for the 12v bus. We ran the servos and cameras off the 6 volt bus.

Short answer, build the IFI circuit.