How to Replace a Battery in a BMW 325I

Removing the Battery
1. Open the trunk. Locate a plastic cover at the back of the trunk on the passenger side. Remove the two small plastic screws that secure the cover with a slotted screwdriver. Lift the cover off the battery compartment.
2. Remove the terminal clamp from the negative (black) battery cable with a 10mm open ended wrench. Pull the clamp off the battery terminal.
3. Remove the positive (red) cable from the battery in the same way.
4. Attach an extension and a 10mm socket to a socket wrench. Reach behind the battery to its base and remove the retaining bolt and retainer. Hold the battery with both hands, then carefully lift it out of the compartment.
Replacing the Battery
5. Purchase a fully-charged battery with the same dimensions, amperage rating and cold cranking amp rating as the one you removed. Place the battery into the compartment, then install the retainer and retainer bolt.
6. Attach the positive (red) cable clamp to the battery terminal and tighten the nut.
7. Attach the negative (black) cable clamp to the battery terminal and tighten the nut.
8. Replace the compartment cover and install the plastic screws. Close the trunk, then start the engine to test the new battery.