On my 95 E420 it lasted 7+ years and was the original Mercedes battery. This being my first MB I was nervous when one day I pulled up to a stop sign on a hill, and did sort of a slow, rolling stop, then hit the gas. Well, several lights on the dash came on, I believe one being the SRS, and I thought oh no what now!. A couple of weeks later it was slow to crank so I took it in for a check and sure enough battery was on last legs. pretty good though vs other cars I have had where battery maybe lasts 2-3 years.

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95 E420 ( 76K) SOLD
85 380SE(125k)
95 SL500(72k)