It sounds your case may be the battery, but I had similar issues with my 4.4 N62 and in my case it was the alternator. I always got faulty alternator code including low voltage codes for nearly every module, but, strangely, no alternator light! The alternator wasn't charging the battery fully and it would intermittently cut out. It was very dangerous as the car could die on the freeway - it did that once and really freaked me out. I replaced the alternator (about $300 for a rebuilt one) and battery. All has been well since.

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'05 E53 X5 4.4i, '97 E39 528, '07 E92 335i, '16 F86 X6M.