It's always these prices here....
I have seen the following online;
Mercedes SL Car Battery 35ah 540cca 230 541 00 01 | ABS Batteries
That isn't much of a battery to turn over a 55k engine
Ideally you need this one with 95Ah and 850CCA
Varta G14 AGM Stop Start Car Battery (595901085) (019) | ABS Batteries
Or this one
Bosch S5013 Car Battery (600 402 083) (019) | ABS Batteries
I got this one sometime back, just replaced under guarantee and its not really powerful enough.
Bosch S5008 Car Battery (577 400 078) (096) | ABS Batteries
Whatever you choose could be more expensive, with shipping, than getting one from your dealer.