what to do if my BMW 3 Series E90/E91 (2005-2012) battery dies overnight

Solution

1. Preparation

• Gather tools and materials including a multimeter, wrench set, cleaning brush, and battery terminals.
• Ensure the vehicle is parked in a safe area and the engine is off.
• Disconnect the battery by removing the negative terminal first.

2. Clean and Secure Battery Connections

• Inspect battery terminals for corrosion.
  • Use a cleaning brush to remove any corrosion from the battery terminals and cable ends.
• Securely tighten the battery terminals to ensure a good connection.
  • Use a torque wrench to tighten to manufacturer specifications (typically 10-15 Nm).

3. Replace the Battery (if necessary)

• If the battery voltage is below 12.4 volts, consider replacing the battery.
  • Use a battery removal tool to safely disconnect and remove the old battery.
  • Install the new battery by connecting the positive terminal first followed by the negative terminal.
• Ensure the battery is secured in place.

4. Address Parasitic Draw (if identified)

• If a parasitic draw is present, identify the circuit causing the issue by pulling fuses one at a time.
• Once the problematic circuit is identified, inspect components for faults (e.g., lights left on, malfunctioning modules).
• Repair or replace any faulty components.

5. Test Charging System

• Start the engine and measure the alternator output with a multimeter.
  • The voltage should read between 13.7 to 14.7 volts.
• If the alternator is not producing adequate voltage, consider replacing the alternator.