Yes, get the battery tested (best if tested in the same temperature). I have had a battery died on me suddenly (not on the X). On my previous daily driver, the car was running perfectly for several hours prior, but would not even crank after just about 30minutes of sitting in the garage (this was in 70*F SoCAL weather) - needed a jump to get it going - going straight to getting it replaced.

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2004 X5 3.0i
Born 02/04
Delivered 03/04