my BMW 3 Series G20/G21 (2019-2024) battery keeps dying overnight, why?

Solution

1. Preparation

• Tools Required: OBD-II scanner, multimeter, socket set, wire brush, safety gloves.
• Disconnect the battery negative terminal to ensure safety while working on the electrical system.

2. Clean Battery Terminals

• Remove the battery terminals using a socket set.
• Use a wire brush to clean any corrosion from the terminals and battery posts.
• Reattach the terminals securely and ensure they are tight.

3. Replace the Battery (if necessary)

• If the battery voltage is below 12.4 volts after charging, consider replacing the battery.
• Remove the old battery by unbolting it from the bracket and disconnecting any connected cables.
• Install the new battery by connecting the positive terminal first, followed by the negative terminal, and securing it in place.

4. Address Parasitic Draw

• If excessive draw is identified, systematically disconnect fuses while monitoring the multimeter until the draw is eliminated.
• Identify and repair or replace the component responsible for the excessive draw.

5. Inspect and Repair Alternator

• If the alternator is not providing sufficient voltage, remove it using a socket set.
• Inspect the alternator belt for wear and replace if necessary.
• Install a new or refurbished alternator if it fails the test, ensuring to torque bolts to manufacturer specifications.