A voltage test does not rule out the BST - a voltage test requires near-zero amps - a crank requires over 200A.

Put a jumper cable from the battery+ to the jump terminal under the hood or the large + terminal in the trunk. If the car starts, the BST or cables are bad.

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Wayne
2005 BMW X5 3.0d (b 02/05)
2001 BMW F650GS Dakar (b 06/01)