hey in my other thread about the 180 size motor and upgrades i talked about using a low voltage drop regulator to control voltage and current to the radio assembly. this type of regulator would limit the voltage and curret when the voltage from the batteries are as low as .45 v above the required voltage, i.e. 5.45 v needed to regulate 5v @ 500ma. i have been thinking of setting up a circuit where a group of 6 six cells are made in to 2 custom battery packs and then put in parralel with the motor and radio w/regulator, batteries in the center
(bad ascii art)
# # #
#(radio)---<<5v@500ma--#(regulator)---#<<(battery)>>(fets)
# # #

I think this would allow running of the lights w/o blowing the board. i testes the xmods board to find out the max current draw
and here are the results
car on, no servo motion(including holding the wheels straight) the car draws about 22ma, with servo moing back and forth it draws about 100-130ma, and with the servo holding wheels against an opposing force the board w/servo draws about 130ma with spikes upto 150ma, so 500ma should EASILY run the radio and lights, i choose 5v because it's a standard value for voltage regulators. now the problem is SPACE!!

FYI i hooked up the gate of the p and n channel fets that form the h-bridge to a scope to test for the BW needed for the mosfets and the board(ESC) switches from 3.5 to 5v @356hz, just like wedginator said