Battery in luggage compartment behind side trim panel
WARNING: This page is about a different car, the 2013 BMW 550i GT, 2012 BMW 550i GT, 2011 BMW 550i GT, and 2010 BMW 550i GT. However, it is still accessible from the selected car via links, so may be relevant.
Remove side trim panel.
Follow instructions for disconnecting and connecting battery.
Disconnect and cover battery negative lead.
Release front side trim panel partly and fold forward.