What are the Ampere-Hour ratings of the main and APU batteries?

• A. Main Battery - 20 Ah; APU Battery - 50 Ah
• B. Main Battery - 15 Ah; APU Battery - 40 Ah
• C. Main Battery - 17 Ah; APU Battery - 43 Ah
• D. Main Battery - 25 Ah; APU Battery - 60 Ah

Answer: (C)

Ampere-hours measure how much total charge a battery can deliver over time, which matters for how long it can power cockpit systems and start the APU without external power. In this aircraft setup, the main battery provides essential cockpit power during start but handles lighter, short-duration loads, so its capacity is smaller. The APU battery must supply enough energy to crank and start the APU and support essential systems if other power sources aren’t available, so it has a larger capacity.

That’s why the correct values are a main battery of 17 Ah and an APU battery of 43 Ah—the main battery is the smaller, quick-power source, while the APU battery is the larger reserve needed for starting the APU and sustaining critical loads. The other options would imply capacities that don’t align with typical start-load requirements and the need for a more substantial energy reserve for the APU.