automotive store. I check mine myself at least once a month and the fluid level. One of my Mercedes is a 99 C280 which I bought Starmarked 4 years ago this May. I am on my third battery. the latest one has lasted over a year. where the one that cam with the car failed in 6 months, no warranty replacement by the way. Mercedes has a two year, pro rated warranty on batteries. But with my MBCA and a little haggling with the parts department I paid $89 for the second one, which failed in 8 months, and the third was prorated to $69. I got two stories why they failed so fast, both from the dealer. One was Mercedes had a supplier in Hungary and the batteries weren't up to spec, now they are outsourced in Spain. The last one was made in Spain, "on the plain." The other was I don't drive the car enough, which is true.
My other Mercedes is a 79 450SLC. The previous owner bought a Sears Die Hard. back in August. I bought the car in October. Maintenance free and so far so good. Only problem was he bought a battery box for it and the hold downs weren't wide enough so I jury rigged some bunggie straps crisscrossed the box and now it is solid. Never have a battery not secured, if it tip over, you could be in for some really problems.
