Last 50cc that I built, I only used one battery for the reciever/servos. If you want a safety margin, could you two. No powerbox. I do tap the power wires out of the regulator and into the servo's power wires. I just cut the positve and negative wires and solder them together. Juice comes into the splice and goes to the servos and receiver at the same time. This way the receiver doesn't have to distribute power. More work, but cheaper and no powerbox or whatever to fail. I use a choke servo for kill reasons. Was going to go Opti, but have read that some have brought planes down. They are not cheap either. Simple choke servo works for me and has not failed me.