I've been asked about BECs (Battery Eliminator Circuit) so here's a little about them: BEC's purpose is to eliminate the need of separate receiver battery. It's connected between the lipo and the receiver. It lowers the lipo voltage, say 11.1 V, to about 5 V that receivers (and servos) use. Speed controllers (and sometimes even receivers) have integrated BECs and normally you don't have to worry about them. But if you use a higher voltage lipo (that is you need a larger voltage drop) or a lot of servos (meaning the servos draw a lot of amps), you may need a separate higher performance BEC.