why is my BMW 5 Series F10/F11 (2010-2017) battery dying overnight

Solution

1. Preparation

• Gather tools and parts required.
• Ensure the vehicle is parked in a safe, well-ventilated area.
• Disconnect the negative terminal of the battery to prevent electrical shock.

2. Inspect and Clean Battery Terminals

• Sub-steps:
  • Remove the positive (+) and negative (-) battery cables.
  • Clean the terminals and cable ends using a wire brush and a mixture of baking soda and water to remove corrosion.
  • Dry the terminals and reconnect them securely.
• Tools Required: Wire brush, baking soda, water, wrench set.

3. Perform Parasitic Draw Test

• Sub-steps:
  • Disconnect the negative battery cable.
  • Connect a multimeter in series between the negative battery post and the negative cable.
  • Ensure all doors are closed and wait 15 minutes for modules to go to sleep.
  • Check the multimeter reading; it should be below 50 mA.
  • If the reading is high, pull fuses one by one to identify the circuit causing the draw.
• Tools Required: Multimeter.

4. Inspect Electrical Components

• Sub-steps:
  • Check for any lights or devices that may be remaining on (e.g., interior lights, trunk light).
  • If any devices are found to be faulty, repair or replace them.
  • Ensure all doors and the trunk are fully closed during testing.
• Tools Required: Basic hand tools.

5. Test Alternator Output

• Sub-steps:
  • Start the engine and measure the voltage at the battery terminals with the multimeter.
  • Voltage should increase to around 13.8V to 14.5V if the alternator is functioning correctly.
  • If output is low, inspect the alternator for faults and consider replacing it if necessary.
• Tools Required: Multimeter.