Hi recently got a message about an Auxiliary battery malfunction for my C200 (late 2014) - does anyone know where can we buy the right battery for this model? I live in Canberra if anyone could recommend it, please?

 

That's a W205 you've got, not W204, so your post is in the wrong section.
https://mbworld.org/forums/c-class-w...on-solved.html shows what needs to be done (it's still on the passenger side on a RHD car, most of the stuff inside the car is mirrored).
https://www.ebay.com.au/itm/Voltage-...-/223843686276 or search Ali for A2059052809 if you don't mind the wait.