Let me clarify. The construction of the Starter battery is standard. Yes, it is unusually small, but any 12-volt battery that can physically fit in its place and can source the proper CCA is an equivalent replacement for the original battery.

The Systems battery is different. It is a unique "Absorbant Glass Mat" (AGM) design which offers superior performance to conventional batteries. Benefits include longer service life and better "deep cycle performance", according to M-B. So, while Autozone will sell you a Duralast battery to replace your Systems battery, it is likely going to be a conventional lead-acid battery and not an AGM. It will work just fine, but it is inferior to the battery sold by the Mercedes dealer.

Some of the "Optima"-branded batteries may be AGM.

__________________
For Sale: many used R129 parts from a white '92, black interior. Send email if interested.