What is the primary function of Battery 1 during engine start?

The primary function of Battery 1 during engine start is maintaining essential systems. This is critical because during the engine start process, the aircraft requires stable power to keep vital systems operational. These systems include flight instruments, control systems, and potentially some essential avionics that ensure safety and operational capability as the engines initiate and build up to operational speed.

While avionics, auxiliary systems, and environmental controls are important components of the aircraft's operation, their power requirements are generally addressed by the main engines or generators once they are running. During the critical moment of engine start, Battery 1’s role is to ensure that the essential systems remain active and functional, thus supporting a safe start-up procedure and transition to generator power.