Originally Posted by Skylaw

They may be in the same size group (49) but not the same battery. Because my '05 is showing signs of a weakening battery, I priced those too - at around $289.

BTW - one sign of a weakening battery is strange electronic "glitches" popping up that go away after shutdown and restart, or actuating a switch. While driving on a 400 mile trip recently, I got an "ESP" warning light after turning up the volume on my radio (drawing more power). I stopped, shut down, re-started, and the light went out and stayed out without my touching the ESP switch on the dashboard. Later in the trip, waiting for passengers, I shut down the car, leaving the music on. The volume decreased slightly - not a lot, but noticeably. It came back up when I re-started. Not much doubt - that battery is beginning to go (it is 5 years old and I drive only a few days each week - a battery killer, as you'll be able to tell from the articles below).

The MB battery for the SL is lead-acid, with a silver/calcium coating on the plates. The MB S-Class battery, I am told, is an Absorptive Glass Mat (AGM) design. I don't know if it has spiral-wound plates.

I found http://batterystuff.com/knowledge-ba...=article&id=11 to be helpful in discussing battery technologies. http://batterystuff.com/knowledge-ba...n=article&id=5 gives a quick rundown on AGM vs Gel batteries. This article is also excellent, and explains the considerations in changing from one battery technology to another in your car: http://landiss.com/battery.htm - mainly, be sure your charging system is matched to the battery!

My dealer parts guy assured me that MB batteries are manufactured by MB in Germany. He said, however, that MB uses Interstate brand distributors to store and distribute batteries to MB dealers in the U.S. I believe that's a fable. Johnson Controls manufactures Interstate batteries (in fact, in the U.S. there are only 2 manufacturers - Johnson Controls and Exide - who make all the battery brands sold here). Johnson Controls also wholly owns Interstate, and manufactures batteries under the seller's specifications for other brands. My MB-branded battery is identical in appearance to an Interstate battery with the same CCA rating and size - except it has an MB sticker and part number. I am sure it was made by Johnson Controls for MB - whether in Germany or the U.S. - and is indeed sold to MB dealerships through Interstate Battery distributors. I would not have hesitated to install an Interstate branded battery in my SL. However, the price difference was zip, and MB Roadside Assistance made the whole proposition very attractive.