The battery in the 2004 BMW 325xi is notoriously difficult to locate, not only because of its non-standard position, but also because BMW positioned terminal posts for jump-starting and testing the electrical system in a different location. Whether you access the battery or the terminal posts depends on whether you need to access the battery's current or the battery itself.
Before accessing the battery, determine what you need from the battery. Do you need to access the physical battery to replace it or remove power to the BMW's electrical system? Or do you need to access the current from the battery? This assessment will determine where you access the battery or battery terminals as well as the convenience for when and where you will do the work.
Since the physical battery is located in the trunk, accessing it to jump-start the engine may not be convenient. If you need to access the physical battery to replace it or otherwise check for corrosion, you should clear the trunk first, especially on the right side, where the battery is located. Also be aware that if the battery is dead, you must use the key to open the trunk since the internal release will not have power.
After clearing the trunk of obstructions, locate the panel on the right side of the trunk that covers the battery compartment. Turn the knob on the panel to release the lock and then remove the panel. If you need to remove the battery, you can remove the clamps on the battery posts and then remove the clamp that holds the battery in place.
If you need to access the battery's electrical current, you can tap into it with the jump-start terminals located in the engine compartment. The positive terminal is marked with a red strip on a cable leading into a small black box on the passenger side of the car. Remove the cover on the black box to access the positive terminal. You can access the negative terminal, which is indicated with a black strip leading into another black box, or you can connect to any other bare-metal grounding point on the car.
