What is a key feature of the "battery bus" in an aircraft?

The battery bus is a crucial component in an aircraft's electrical system. Its defining characteristic is that it remains connected to the battery at all times, even when the master switch is turned off. This design allows essential systems and components to receive power directly from the battery without needing the master switch to be in the on position.

This persistent power supply is vital for functions like keeping certain avionics and emergency systems operational when the aircraft is not powered by the main electrical system. In circumstances where the engine-driven generators are not operational (such as during engine failure or ground operations without the engines running), the battery bus ensures that critical systems can still be accessed.

While other options such as emergency lighting, avionics power during flight, and control of fuel pumps are important aspects of an aircraft's electrical system, they do not accurately describe the continuous connection feature that makes the battery bus unique.