What is the purpose of the external power receptacle?

The primary purpose of the external power receptacle is to provide power to the avionics systems of an aircraft when the engines are not running or when there's a need for additional power. This allows ground crews to operate critical systems like navigation, communication, and other electronic equipment without relying solely on the onboard batteries. By connecting to an external power source, these systems can function continuously, ensuring that the aircraft is ready for operations and maintenance procedures can be performed without interruption.

While charging the onboard battery and supplying power to ground support equipment can be important functions, the core role of the external power receptacle is specifically to support avionics systems during ground operations. Discharging excess power does not align with the function of the receptacle, as it is designed to draw power rather than release it.