My battery is 4 months old (genuine MB) and using the climate control lcd I usually have 13.9-14.1 volts. I never drive like Schumacher in my S-class so I dont think I am overfueling (running rich) but I think that the sulfur deposits in the catalytic converter are heating up and burning away. I was on my way to San Diego, so I would assume all the components were getting pretty hot. My temp was at a steady 100C IN 75f ambient weather. I also remember the same smell once I was driving to Las Vegas with similar passenger load. Anyways, Ill go to Benz tomorrow and keep you guys posted.