What function does the right battery serve during APU start?

The right battery's primary function during APU (Auxiliary Power Unit) start is to operate the APU starter. The APU is often used to provide electricity for onboard systems and to assist in engine starts. During the starting process of the APU, it requires a significant amount of electrical power, which is supplied by the right battery. This is crucial because without adequate power, the starter may not function effectively, hindering the APU's ability to start.

Understanding this role helps reinforce the importance of battery systems in aircraft operation, particularly during critical phases like starting auxiliary systems. The options relating to power for the main engines, charging the generator, or powering ground services do not apply directly to the APU start process, which is specifically reliant on the starter function powered by the battery.