why does my Volkswagen Passat B8 (2015-2022) battery drain overnight?

Solution

1. Preparation

• Gather tools: OBD-II scanner, multimeter, wrenches, and basic hand tools.
• Ensure the vehicle is parked in a safe area with the engine off and keys removed.
• Disconnect the negative battery terminal to prevent any electrical shorts during the inspection.

2. Inspect Battery and Connections

• Sub-step 1: Clean battery terminals using a wire brush to remove corrosion.
• Sub-step 2: Tighten the battery terminal connections to ensure a secure fit.
• Sub-step 3: Check the battery condition. If it is more than 3-5 years old, consider replacing it.

3. Perform Parasitic Draw Test

• Sub-step 1: Reconnect the negative battery terminal.
• Sub-step 2: Set the multimeter to measure current (amps) and connect it in series with the negative terminal and the battery.
• Sub-step 3: Wait for a few minutes for the vehicle systems to go to sleep, then note the current draw. It should be below 50 mA.
• Sub-step 4: If current draw exceeds this limit, proceed to identify the circuit causing the draw by removing fuses one by one until the draw drops.

4. Repair Identified Issues

• Sub-step 1: If a faulty component is identified, repair or replace it accordingly (e.g., repair wiring, replace relay).
• Sub-step 2: For excessive draw from an accessory, ensure proper installation or disconnect it if necessary.

5. Finalize and Test

• Sub-step 1: Reconnect all fuses and ensure all connections are secure.
• Sub-step 2: Reconnect the negative battery terminal and perform a final voltage check to confirm the battery is holding a charge.
• Sub-step 3: Test the vehicle by starting it and checking for proper operation of all electrical systems.