If the aircraft is only running on battery power, what is lost?

When an aircraft is solely relying on battery power, it indicates that the auxiliary electrical systems may be functioning without the benefit of the engine-driven alternators. However, in terms of what is lost, the option indicating that "nothing" is lost may suggest that the essential systems critical for flight operation can still be maintained, albeit with limitations depending on how the aircraft is configured.

If the situation is controlled properly, the essential flight instruments, navigation systems, and communication systems can often still be operational on battery power alone, at least for a limited duration. This implies that while the battery life would be a concern, the aircraft's essential systems do not cease functioning immediately but rely on the battery until it discharges.

It's important to underscore that the restrictions on functionality could vary based on the type and configuration of the aircraft, but in a general sense, the assumption when running on battery is that some basic operational capabilities remain intact, allowing for continued flight.