How do you change the battery on a 2004 BMW 3 series?

Answer 1

All E46 Models from 1999 through 2005 are basically the same. First off have the presence of mind to record your radio channels since some models of the radio will loose them all when you disconnect the battery. Now get some safety glasses and put them on.

The battery is in the trunk on the passenger side under a panel that makes up the load floor. Some cars you can simply lift this panel up and out, but others, like my wagon requires you to remove the adjacent side panel (look for a rectangular button at the top of the side panel if this is the then push it and the panel will unlatch and move toward you). After the floor plate is removed you will see the battery.

Using a 10 mm wrench remove the negative terminal clamp. Always disconnect the negative first and reconnect it last. It will help you avoid blowing up the battery. This is also a good reason to be wearing safety glasses. Then, using the 10 mm wrench remove the positive terminal. It has a large bulge and more than the one wire since it has an emergency disconnect that severs the electrical connection if an airbag goes off.

The battery is clamped down by a large Philips screw. Unscrew it enough that it turns easily. Then you can remove the 10mm bolt that holds the battery and this clamp plate to the car. Some models have a large plastic floor support that interferes with this so you may have to use a small (8 or 9 mm) wrench to remove the two screws that hold this plastic piece in place. Once the bracket and the plastic are out of the way you can lift out the battery. I suggest using a battery carrier to get it out (the ones that simply slip over the terminals are cheap and work well). Careful though, this is a heavy battery to sustain all of the electric gizmos that these cars carry.

Installation is the reverse of above. Be sure not to over tighten the plastic bits and always attach the positive before the negative.