I would eliminate the battery as a cause first. Easier to do and little or no cost. Also, more likely to be the problem, especially if it is over 3-4 or more years old and you drive mostly short distances or you don't drive it much. Most places that sell batteries will test it for $0.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas