any battery that can be mounted to on it side or that is sealed does not to be vented like an optima yellow top. the batteries that mercedes supplies with the car is a lead acid battery. you can check how low the fluid level is and top it off as needed. with the optima's the use a sealed design that doesn't use lead acid. some batteries use gel cell technology, these you can mount upside down and still work. you cant do that with a lead acid battery, acid would spill all over the place and corrode everything. all though these batteries are expensive, they usually last longer.
hope this helps.