Where is the battery on a 2005 BMW 525?

The battery is located in the trunk to the right side. There is a large caperted panel that covers access to the brake light assembly, the fuse block, and the battery. you'll need a flat head screw driver to remove the plastic retainer clips. Raise the spare tire cover and hold it up as you pull the carpeted panel away from the body. (takes a little effort) once exposed you'll need a 13mm socket to remove the bracket which goes the length of the battery and a 10mm socket to remove the battery hold down bracket and to loosen the battery terminals.