When weird electrical things start to happen, I always suspect the battery first and the alternator second.

You can see what battery voltage is with the car off (for a while so it goes into sleep mode) and it should be 12v or a little more. While running, you'd like to see 14v at the battery.

Many parts shops (pep boys) or Sears/KMart auto centers will test your battery and alternator for free.

If it is your battery, I recommend getting an absorbed glass mat (AGM) replacement battery. I bought this one: Deka AGM battery

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Kirk
Las Vegas
2016 X5 40e Mineral White/Black Dakota Leather, ZLL, ZCW, ZDA, ZDB, ZPP, multi contour seats, rear side window shades, HK stereo
2011 E90M3, 6-speed manual