I also use a 7.2v pack, but made of 2 LiFe cells (DeWalt A123 batteries), in my IOM. I use a CC BEC voltage regulator, set to 6v, to run the RX and rudder servo, but the sail servo gets the full 7.2v. My next IOM will use the winch that will supply the RX and rudder with 6v.

My Victoria uses a 5 cell AA NiMH pack at 6V nominal.