Hmm. Can't say exactly. You are getting an IBS message which is interesting. I don't recall having any codes like yours but then again my problem may never have been the alternator in the first place. I had a bad ground strap as I mentioned but replaced the alternator in the process.
If it were me I'd really look into the IBS, then the alternator.
https://www.bimmerscan.com/bmw-intel...ry-sensor-ibs/
https://www.newtis.info/tisv2/a/en/e...ttery/1LyvW9MF
"...only exchange the IBS when there is a corresponding fault code entry!"
BMW is pretty clear on not replacing the IBS unless its actually the problem. They say in one of those articles that they've tested "defective" devices that were replaced and they were fine. Unfortunately I'm not sure how to determine whether its defective or not.