Which aircraft electrical system component provides back-up power?

The component that provides back-up power in an aircraft electrical system is the battery. The battery plays a critical role in ensuring that essential systems continue to operate in case the primary power source, typically the alternator or generator, fails or cannot provide sufficient power.

When the aircraft is on the ground or during take-off and landing, it is often the battery that initially supplies the electrical power for starting the engines and powering avionics before the alternator begins operating once the engine is running. In the event of an electrical failure, the battery can provide enough power to maintain vital systems such as communication devices, navigation instruments, and emergency lighting.

This functionality is essential for safety and operational reliability, as it allows pilots to maintain control and communicate during critical phases of flight, particularly if there is a loss of power from the primary source.