I would still try to jump the vehicle to make sure it isnt a battery problem. Because even with a new battery you may have a parasidic draw that could be draining your battery.
If the jump start doesnt help I have some more ideas of what could be the problem.
BMW Technician
BMW Master Certifed level 1 Technican
It could still be the starter but I would like to eliminate the basics first. There are jump points under the hood. The negative point is located on the right strut tower, The positive I think is either near the negative jump point on the strut tower or on the top of the intake manifold there was a midyear change. The positive jump point should be cover with a plastic cap with a red plus sign on it.
The starter is about $200 and is 4 hours of labor average shop rate is $100 per hour, so about $600 total.
If the vehicle doesnt start I would suspect the starter.
This is no problem for me, please keep asking questions until it is fixed it is what I am here for.
Yes alternator are common problems on 525i. I think a bosch part is a great idea I would avoid the regular parts stores alternators as well. I recommend a BMW unit but the choice is yours a good website is www.getbmwparts.com
The alternator does make perfect sense for the problem.
Glad to hear you have got to the bottom of your problem.
Thank you