The battery in your car has a higher capacity than anything readily available in the US aftermarket. Optima battries are wonderful for racing, but not suitable for a Mercedes car, and a tremendious waste of money.
The good news is that a proper battery can be purchased from Roadside for about the same you would pay at Sears. It will have the correct capacity, fit the spot correctly and have the right weight, as envisioned by the engineers.
They come to you and install the battery for free. The technician will also check everything that needs to be reset.
Look on your visor for the telephone number.