I run two 1100mah a123 on two switches with 4 power leads running to wyes and the rx for flight controls, and 1 1100 mah a123 for the ignition. One charger does the whole plane. Same weight as a single 2500 with redundancy. The need for multiple connections is because the batteries can put out in excess of 30 amps each but a standard servo connector can only handle about 4 amps each. 22ga wire can handle burst of 20+ amps. A 50cc plane can draw in excess of 20 amps in some maneuvers.
Currently I'm flying my EF Yak on one 1100 mah a123 and get 3 flights between recharges. About 8 flights on the ignition. I'll be putting the other battery in there soon though.
On my setup the elevators get 1 power lead, the Ailerons and rudder also get a lead each and one to the rx. To explain, where you plug the servos into the rx is a buss bar. The red and black wires are + and - and are continuous through out. By making wyes you provide more ways to connect power or extra servos. Just make sure you don't connect to the white, or signal wire. I use the optic kill switches. Very easy to install and they work.
I could be wrong but I believe AMA requires an onboard engine kill system for gas engines. I do not think cutting the throttle or choking it dead are concidered on board kill devices, but if someone knows different please let me know.