When I replaced the battery in my 01 X5 it didn't resolve the dead battery issue. Turmed out to be a final stage resistor problem. Hope that's not the case here. You would think BMW resolved that problem in the E70 series. I think I will replace the battery though, just to be safe.

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2007 X5 4.8i Space Gray
2001 X5 3.0 Titanium Silver