The Battery Alternator Visit Workshp light comes sporadically. I stopped by an auto parts supplier who tested both the battery and alternator. Both tested good. I've read that this warning light is usually caused by a faulty voltage regulator. If the VR is going bad, wouldn't this show up as a faulty alternator? My 2005 C230 has 120,000 miles, original battery and alternator, the belt was replaced aprox 30,000 miles ago and looks to be in excellent condition. I don't mind replacing either the batter or alternator, but hate to if not needed. Any suggestions?