When engine is off what powers the radio?

When the engine is off, the radio in a car is typically powered by the vehicle's battery. Most modern cars have an electrical system that allows the radio to continue to operate for a period of time even after the engine has been turned off. This is done by using a relay or other type of switch to connect the radio directly to the battery. When the engine is turned on, the alternator recharges the battery and provides power to the electrical system, including the radio.