What is the primary purpose of the aircraft battery during normal operations?

• A. To regulate the DC bus voltage continuously.
• B. To recharge the generators after start.
• C. To supply high-inrush current for starting and to provide a power reservoir if generators are offline or during faults.
• D. To power avionics during flight.

Answer: (C)

The key idea is that the aircraft battery acts as a ready energy source to handle starting and to back up the electrical system if the normal power sources are unavailable. Engine starts draw a very large inrush current, which the battery supplies so the starter and related systems can operate reliably. Once the engines and generators come online, the generators take over and the battery is recharged, ready to respond to the next demand. The battery also provides a buffer during faults or generator outages, helping to keep essential systems powered without a sudden voltage drop.

Regulation of the DC bus voltage is accomplished by the generator voltage regulators and the overall power-management system, not by the battery itself. While the battery is recharged after starting and can provide temporary support if necessary, powering avionics continuously during flight is the function of the bus powered by the generators, with the battery serving mainly as a backup and starting aid rather than the primary power source.