Which battery powers the APU starter motor?

• A. APU Battery powers the starter
• B. Main Battery powers the starter
• C. Both batteries power the starter
• D. External power powers the starter

Answer: (A)

The APU starter motor is powered by the APU’s own dedicated battery. This battery provides the high-current surge needed to crank the APU without drawing from the main aircraft electrical system. Having a separate APU battery ensures the APU can be started independently, even if the main battery is in use for other critical systems or if buses are not yet online. The main battery serves other essentialStarts and loads, so relying on it for the APU would risk draining it and potentially affecting aircraft systems. External power can supply power on the ground, but it isn’t the energy source for the APU starter during normal operation; it’s used for ground power when needed rather than to drive the starter itself.