On the m54, the starter is on top of the engine it will be easier to steal somebody else's X5 than get power there and the stiffening plate will be in the way of accessing the alternator.

I'm wondering however if one of the main power feeds is accessible under the car, I seem to recall bumping into a large red cable under my client's 328xi.

Unless you can turn the key 90° to unset the double lock you will not be able to open the door directly.

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)