DIY Battery Replacement for a BMW 3


1. Decide whether to buy an aftermarket or an original equipment manufacturer (OEM) battery based on your budget and preference. Purchase a replacement battery from an auto store or BMW dealership.
2. Open your BMW 3-series trunk and remove all stored items. Pull up on the spare tire cover to remove the cover and spare tire. This allows access to the battery cover on the right-hand side of the trunk.
3. Remove the two plastic screws that are holding the battery cover in place with a Phillips head screwdriver. Place the screws aside for re-installation. Lift the battery cover off and set it aside. The battery is now exposed and ready to work on.
4. Locate the positive terminal on the battery, which has a red cover with a '+' sign on it. Pull the plastic red cover off the positive terminal with your hands to remove it. Loosen and remove the bolt underneath the red cap with a 10 mm wrench to release the red connected cable.
5. Locate the negative terminal, which has a black plastic cover with a '-' symbol on it. Pull the plastic black cover off the positive terminal with your hands to remove it. Loosen and remove the bolt underneath the black cap with a 10 mm wrench to release the black connected cable. Place the cables aside so they don't interfere with the rest of the job.
6. Unscrew the tall screw in the front of the battery that attaches the battery to the bottom of the battery tray, using a Phillips head screwdriver. Set the screw aside for re-installation. Pull the battery up to remove it from the battery tray. Place the battery aside for disposal.
7. Place your new battery into the battery tray. Screw the tall screw into the front of the battery with your Phillips head screwdriver to attach the battery to the battery tray.
8. Reattach the red positive and black negative cables to their respective positions with the 10 mm wrench. Replace the red cap on the positive cable and the black cap on the negative cable.
9. Place the battery cover over the battery. Screw in the two plastic screws saved in Step 3, using your Phillips head screwdriver.
10. Replace your spare tire and spare tire cover over the battery cover and push it into place. Close your trunk.