I have a 2010 e550 Mercedes the Auxiliary Malfunctioning light message comes on what is the solution.
Thanks
John

Mercedes-Benz cars have two different type of auxiliary battery also known as Mercedes secondary backup battery, it completely depends on the car model, year and many other specifications.

So the first step is to check which battery is used in your Mercedes by opening a hood (bonnet) and trunk (boot), in the trunk this part is usually located nearby fuses if after inspecting these two places you weren't able to locate small auxiliary battery it means your car uses voltage converter.

Auxiliary battery is responsible for running and powering additional accessories in the car such as stop go function and many other, once it detects failure none of these functions will work.