On the Airbus A320, the BAT 1 and BAT 2 switches are located on the overhead electrical panel. These switches control the connection of the aircraft’s batteries to the electrical system. Here’s how they function and are used:

Purpose of the Battery Switches

1. BAT 1 and BAT 2 connect the aircraft’s two main batteries to the DC electrical system.

2. The batteries are used:

   • During APU start.

   • As a backup power source in the event of a loss of AC power.

   • To power essential systems during a complete electrical failure.

Operation of the Battery Switches

1. Switch Positions:
   
   

   • ON: Connects the battery to the DC electrical system via the Battery Charge Limiter (BCL).

   • OFF: Disconnects the battery from the electrical system.

2. Normal Procedure:
   
   

   • During cockpit setup, the BAT switches are turned ON as part of the preflight checklist.

   • The batteries remain connected to the system during normal operations, allowing them to charge from the aircraft's generators or external power.

APU Start

• The batteries are critical for starting the APU (Auxiliary Power Unit).

• During APU start, the batteries supply power to the APU starter motor until the APU generator becomes active.

Monitoring Battery Status

1. Battery voltage and charge are monitored on the ELEC page of the ECAM.

2. Normal battery voltage is approximately 24-26V.

   • If the voltage drops below 25V during preflight, the batteries should be charged using external power.

Emergency Use

• In case of a total electrical failure, the batteries power the Emergency Electrical Configuration, including essential systems like:

  • Integrated Standby Instrument System (ISIS).

  • Flight Control Computers (essential for manual control).

  • Communication systems.

The battery switches are a vital part of the A320’s electrical system and play a key role in ensuring redundancy and reliability during operations.