Vibration Compensating Battery Systems: E46:
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.
The E46 convertible uses the same battery as the E46 sedan, coupe and touring. The battery box is specially designed to float on the vertical axis through three articulated rods.
This allows the battery to act as an inertia mass and dampen various vibrations while the vehicle is driven.