Weird, my OEM battery was still running strong after 8 yrs... I only replaced it because I was having it shipped overseas. FWIW, the OEM Mercedes battery is actually the same as an Interstate. At the dealer it would have been $250, at a tire shop I got the Interstate for $140 (and it's the higher life/CCA version).

Edit: The battery is from 2009, meaning someone already changed it? Is it the correct one?