Which battery is used to start the engine initially, and when does the second battery begin assisting?

• A. Number 2 battery is used to start; Number 1 battery assists at approximately 10% Ng
• B. Number 1 battery is used to start; Number 2 assists at approximately 50% Ng
• C. Both batteries start simultaneously
• D. Battery 2 starts after 90% Ng

Answer: (A)

The starting sequence is designed around sharing the heavy starter current between two batteries. The second battery provides the initial start power to spin up the engine. As the gas generator speed (Ng) comes up and reaches about 10%, the first battery comes online to assist, helping to maintain starter power and share the electrical load as the engine continues to accelerate and the starter drops out. This arrangement provides redundancy and a smoother start without overloading a single battery. Starting with the first battery or waiting until a high Ng before assist would not match the system’s designed handover point, which is around 10% Ng.