I just went through this and here are your options:
1. If $ is not an issue, get an Optima battery or go to the Benz dealer to get one. Expect to pay between $100 - $120.
2. Get the cheapest Group 49 battery (big size) and replace it every 6 or 7 years (the length of the warranty of these batteries). Autozone has one for $59. There are only a handlful of battery makers in North America like Johnson COntrol et al. and many batteries are the same inside.
I got the Autozone for my diesel and it has been wonderful so far (only about a month).