W221 Auxiliary Battery Malfunction

[S350L]

Hi All

I have a 2011 W221 S 350 L cdi Bluetec

Last night, on my way home, the "Auxiliary Battery Malfunction"warning came on. At the same time, the "Distronic Inoperative" warning came on too.

Which battery would this be? I've had a quick google search, as we do, and I am a little confused. Some people refer to the battery in the boot as the auxiliary battery, however, some refer to it as the starter battery, which I thought was the large battery in the engine bay. I have also seen videos (from the USA) referring to the auxiliary battery as one located under the steering wheel.

So, I think my car has 3 batteries. Which would be the auxiliary battery?


Thanks in Advance

 

[AndrewOl]

Big battery (if it’s not an ev) is the starter battery. Aux battery is a smaller unit usually about the size of a house brick. They get squirrelled away in all sorts of places but the boot is favourite under the floor carpet. I’m sure someone with specific model knowledge will pipe up with a bit more detail.