BST Construction
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 an encapsulated pyrotechnic device that is similar to an airbag in operation. The BST contains an ignitor capsule and discharge tube that is mounted in front of the high amperage B+ cable. The B+ cable contains a tapered press fit contact that mounts behind the gas discharge tube.
During activation, the tapered B+ cable contact is forced away from the battery post and held away by spring tabs within the capsule.