BEC - Battery Eliminator Circuitry

A circuit that eliminates the need for a receiver battery, usually in electric R/C cars and boats.

Wiki:
A battery eliminator circuit (BEC) is an electronic circuit designed to deliver electrical power to other circuitry without the need for a battery. Historically the expression was sometimes used to describe devices used to power battery-driven equipment from mains electricity. This is still the case in many products offered in retail electronic supply stores.