If you keep the car registered with Mercedes you should have gotten a letter extending you warrantee to 150,000 miles with the FSS system. I recieved one for my 1999 E300.
If you need a new battery call road side assistance to do it. They carry the batteries ( a diesel and a gas battery. Merceds now only has 2 kinds of batteries)and wont charge you labor for the instalation. If you bring it to the dealer they charge you labor. teh Mercedes battery is the way to go I used Sears batteries for years due to the Mercees cost. They finally got smart and lowered the price. The deisel battery is about $120. The Sears was $119.
Dave

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1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car