What are the amp-hour ratings for the Main and APU batteries?

• A. Main 17 Ah; APU 43 Ah
• B. Main 43 Ah; APU 17 Ah
• C. Main 20 Ah; APU 40 Ah
• D. Main 15 Ah; APU 30 Ah

Answer: (A)

Amp-hour rating shows how much energy a battery can store and deliver over time. In aircraft design, the main battery is sized for delivering high current in short bursts to start engines and to power essential systems briefly when there’s no external power. It doesn’t need a large energy reservoir, so its capacity is relatively modest. The APU battery, however, must sustain power for the APU start sequence and support systems when the APU is running or when ground power isn’t available, which requires more stored energy. That’s why the APU battery has a larger Ah rating than the main battery. With this in mind, a 17 Ah main battery and a 43 Ah APU battery align with the expected roles, making the pair the best match.