'08 535i, 180k miles, N54, original alternator, IBS disconnected for past 5 years w/o issue.

I went to replace my alternator brushes/ voltage regulator as preventive maintenance. Replaced it with Bosch F00M346088. After install, charging voltage went up to ~15.5V (even after a 20 minute drive).

I changed it back to the old regulator and the charging voltage went back ~14.4V.

What am I doing wrong? Do I need to re-register the battery? I tried hooking up the faulty IBS again but it made no difference. Did I get a defective Bosch regulator? Do I need to spend the $130 more for the BMW branded Regulator (12317561939)?

Thanks in advance.

Pic to show 180k of brush wear vs new:

 

If the charging voltage went up to 15.5V that is characteristic of the voltage regulator malfunctioning.

Is it likely the wrong regulator they provide you?

I have a Valeo alternator in my e60. It was difficult for me to find a new voltage regulator when I replaced it recently.

 

I'm leaning towards purchasing another Bosch regulator but I just want to make sure I'm not missing a step. Fortunately, it is easy to swap out.

 

Idea:

My vehicle came with 2 options for the alternator (150 amp unit or 180 amp unit).

Its logical to think your parts supplier either gave you the wrong regulator or the regulator they gave you is malfunctioning?