What is the purpose of connecting external power to an aircraft?

Connecting external power to an aircraft primarily serves to provide electrical power for systems while the aircraft is on the ground. This is crucial for powering various onboard systems that require electricity, such as lighting, air conditioning, onboard computers, and avionics, without relying on the aircraft's engines or batteries. This connection allows crews to perform pre-flight checks, maintenance, and any necessary operations while the airplane is parked, all without depleting the aircraft's internal battery.

While some may think external power is used to ensure readiness for takeoff, the aircraft needs its internal systems functioning while on the ground for pre-flight procedures, which is why supplying power is essential. Charging the internal battery can be a byproduct of using external power, but the primary intent is to provide immediate electrical needs. Enhancing engine performance is not related to external power connections, as engines operate independently during takeoff and flight.