Collision Prevention Assist - low voltage

[BlueRubber]

HI all,

Got a 2013 post facelift S212 e350 and the collision prevention assist inoperative error message on the dash.
Looked in Xentry and as per the attached screenshot it looks like the issue is low voltage at the control unit.
Screenshot was taken with the engine running.
The main car battery was replaced about a month ago and everything else works ok ( other than brake pad warning message ).
Any idea what to do next to fix this?
Thanks

 

[OneForTheRoad]

Shot In the dark here , but is it possible it's powered from the motorbike battery in the boot and it's the battery that's knackered??

 

[BlueRubber]

This did cross my mind but I would assume I would get more warnings from other systems.
I will check the voltage of that battery just in case.