Battery Safety Terminal (BST)
WARNING: This page does not describe the selected car, but rather 151 other vehicles, including the 2006 BMW X5, 2006 BMW M3, 2006 BMW 330Ci, 2006 BMW 325Ci, and 2005 BMW X5. However, it is still accessible from the selected car via links, so may be relevant.
The BST is used to disconnect the battery connection to the starter, alternator and charging post in the event of a collision. This safety measure helps prevents the possibility of a short circuit in the engine compartment causing a fire.
The battery connection to the power distribution box and body electronics is un-affected.