The Lead Terminals
WARNING: This page does not describe the selected car, but rather 208 other vehicles, including the 2010 BMW Z4, 2010 BMW X6 M, 2010 BMW X6, 2010 BMW X5 M, and 2010 BMW X5. However, it is still accessible from the selected car via links, so may be relevant.
BMW's use a tapered top terminal. This design uses tapered terminal posts built to industry standards so that all cable clamps will fit any battery with these posts.
The positive terminal is slightly larger than the negative to minimize the danger of installing the battery in reverse. The positive terminal is 17.5mm in diameter at the top. The negative terminal is 15.9mm at the top.