BEC=Battery eliminate circuit. As the other ching said. It lower the battery voltage to 6V so it is safe for your receiver and servo. If you need / wants to run an external BEC a 3amp unit should be more than enough for one servo and receiver. Can get it at most RC airplane shop for under 100hkd. BTW: Do not forget to remove the red wire from ESC to receiver or you will burn the ESC.......