A battery is a device that chemically stores energy for later use. Batteries have many uses in RC, providing power to the transmitter, receiver, servos, motors, lights, and various other electronics. NiCd and Lipo batteries are most common on board the RC model. NiMH batteries are sometimes used to power transmitters. A123 batteries are also becoming more common for powering RC models. In recent years, batteries have become powerful and small enough to allow the use of electric motors in aircraft as a replacement for gas engines.