Sounds like a battery issue, as has been stated.

Don't just replace the alternator or battery blindly. Both can be tested, usually for free, at Pep Boys or other auto parts place.

__________________
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