i have a 2009 C300 w204 4matic the battery keeps dying. Does anyone know if this car has an aux battery? if so where is it located?
2009 W204 does not have an aux battery.
Try looking for it in the engine bay, passenger side. If it is not located there than it might be located in the trunk on the right side or under the rear side.
If I remember correctly the 2009 W204 does not have an aux battery.