Prior to APU start, the minimum battery voltage must be present on both batteries is

• A. 22V on both batteries
• B. 24V on both batteries
• C. 18V on both batteries
• D. 28V on both batteries

Answer: (A)

Before starting the APU, you need to see a solid voltage on each battery. Specifically, each battery should read at least 22 volts. This ensures the APU starter can draw enough current and the electrical buses stay stable during cranking, even as voltage sags under load. In a typical 24-volt system made from two 12-volt batteries, 22 volts per battery gives a safe margin above the per-cell minimum, preventing a weak or failed start due to insufficient drive or excessive voltage drop. If one battery is below this threshold, the APU may fail to start or experience unstable electrical behavior. The other voltage options don’t fit because 24V is the nominal system voltage, not the required minimum under load; 18V is too low to reliably power the starter and systems; 28V is above normal operating range and unnecessary.