RE: Two battery packs for park flyer???
On a parkflyer, the ESC (Electronic Speed Control) supplies power to the receiver and servos via the throttle channel + and - bus. The ESC has an on-board regulator to supply 5v to the receiver and servos right from the flight pack. You only need to worry about one pack to charge per flight.
There is no real typical voltage for a motor. Use the recommended setup for the the power system or the plane.