I’m dealing with similar issue….
The original alternator failed, replaced with a new one (not OEM) which failed within hours; got a replacement (same model) which lasted 5 days…..
I had put two new ground straps so I hope that is not the issue
No idea what else could be behind - any suggestions?
Note it is an e70

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E70 - 3.0si & F10 - 535ix
Previous Cars:
E34 - 525i, E39 - 530i, E60 - 530i