Dave3359

2017 s550 cabriolet. Does anyone have any idea what the plug on drivers side in the trunk is for??

ron104

That is used to connect an M-B 24 volt battery charger.

Dave3359

So that is a charger port for the rear battery correct? Would you happen to know what the part # is for the battery tender is. Thanks again for your help greatly appreciated.

ron104

The charger part number is: Mercedes-Benz A0009822921.
The charger is used for both the rear battery and the front 12 volt.

Dave3359

Funny thing is I just found a brand new one on Facebook marketplace same part number and it did not fit the plug in the trunk.

ron104

Dave, Sorry to hear that.
The plug only fits one way. Did you try to rotate the plug to the other side?
Mine fits perfectly and I have been using it for 7 years.

Dave3359

Yes tried it every way and rotated it around no joy. Going to the dealer and see it they can figure it out. Also do you know if that outlet charges both batteries or only the auxiliary battery? Thanks again for your help Dave

ron104

As I understand, the rear outlet only charges the rear battery.
However, the front charges both batteries.
Don't ask me how--It's magic!!!!!!

Dave3359

That’s funny because mySL550 I charge The rear battery, and that also charges the front battery. The total opposite.

as.thompson

Is that plug only in 2017 (and later)? No plug in my 2016 C-217 coupe.

Dave3359

I have no idea if the plug is 2017 and on I have A-217 cabriolet. And I sure that makes no difference. Maybe others will jump in

ron104

I have a 2017 cab and it has a plug in the trunk.
I also have a 2019 coupe and it does NOT have a plug in the trunk.