In all cases that I have seen where the battery light is illuminated the alternator is faulty internally and needs to be replaced. The only way the light can come on is by passing current through the contact brushes in the voltage regulator.

------------------
Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
LEAD TECHNICIAN FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM