Which systems are covered by the auxiliary battery?

The auxiliary battery is designed to provide power to critical systems that are essential for the safe operation of an aircraft in the event of a primary power failure. In this context, the correct choice includes standby instruments, standby lights, and UHF. Standby instruments are vital for maintaining situational awareness and safe flight operations when primary displays are lost, while standby lights ensure that pilots have visibility and guidance in emergency situations. The UHF (Ultra High Frequency) radio equipment is crucial for communication in flight, particularly in scenarios where other communication systems may be compromised.

This choice effectively represents the systems that require immediate backup power to ensure continuity of operations during emergencies, which is why it stands out as the correct option. In contrast, the other choices mention systems that either do not prioritize immediate power backup or are less critical in emergency situations.