Phil,
Changing a battery on a Mercedes is pretty straight forward, however, if you do a search on 'battery' on this forum and others, there are some horror stories.
I had my indy do mine when it was in for other services and his test proved out that the battery was near the end of it's life. Had I not had the car there, I probably would have called MBUSA, 1-800-For-MERC, and ask them to dispatch Roadside Assistance to wherever you are. The closest dealer brings you a new battery, installs it, disposes of the old one, and resets your radio w/the code, re-synchs the windows, top, or anything else that may need attention. The last time I looked the fee for this is basically the cost of the MB branded battery; $100-$125. You can ask MBUSA if you call them.
It's also not a bad idea, if you haven't doneso already, to 'register' your car at the
www.mbusa.com site.
One thing I wouldn't do is trust the kid at AutoZone or Wally World to change out one of these batteries. But if you want to DIY read up on the steps in alldatadiy.com for the specifics on your model year.
Bob