I have a 2008 Z4MC with 40,000 miles on it I had the same warning signs that my alternator / voltage regulator was not working. I pulled the alternator and verified that indeed it was a Valeo brand alternator.
I purchased the following part from americanenginesco.com
http://www.americanenginesco.com/bmw...tor-valeo-oem/
1 x BMW 3 Series Z4 3.2L Alternator Voltage Regulator Valeo OEM
Price:$67.85
SKU:9703
Brand:Valeo
I replaced the voltage regulator on my alternator and everything is now back to normal. Took a total 3 hours to remove the alternator, replace the voltage regulator and reinstall on car (in my driveway).
I hope this helps.