As much of a drag as it seems, it would not be unreasonable for an original battery in an 08 to be at the end of its service life. And the replacement won't be warranty covered.
That said, I did have a similar parasitic draw condition in my E53. Even with nothing plugged in, the battery would drain after a few days - usually at the airport where it caused me the most drama.
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-Will
2013 535i xDrive M-Sport | 2005 545i Sport (Retired and missed) | 2001 X5 3.0 Sport (Retired)
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