If your battery died after parked for only 4 days I'd replace it. I have read about some issues with the batteries going south in brand new X3's just weeks old. Even with a light drain from the systems it should keep a charge much longer, like at least 2 weeks if not more.

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'05 X3 3.0i Alpine White/Gray Leather/Alum. Trim
Sport/Steptronic/Servotronic/Panoramic
Prem. Sound/Staggered 18" Style 114 Y-Spokes