Does anyone know how to specify the correct 100 ah battery for a 1996 EE320? For example something like "94R" is what I am looking for .. so I know which one to buy at my local Batteries+. The battery is a heavy long thing and sits underneath the rear seat cushion.

They will be able to look it up for you. It's a group 49 battery. The group number specifies the physical dimensions and location and type of connector posts.

The expensive sealed AGM batteries (I forget the brand name - dang age!) are group 34. They fit OK in a Benz - just a bit taller, much less wide, and same depth as a 49. You need to get one with reverse terminals - used to be the orange top, but is not the reverse red top. I wouldn't bother spending that kind of money on a battery for a gasoline car though - just get the regular lead/acid battery.