Mike,
This stinks about your car.
Other than having another dealer look at it (or at least another set of trained eyes), I'm not sure what to do.

As far as the battery chargers/tenders go; a lot of manuals say not to 'jump' them or put chargers on them, but I've not heard of any issues such as this.
Personally, I remove my battery while the car is in storage and hook it up to a tender, but that is beside the point.

They might need to replace the PCM/ECU, if they haven't done so already.

Best of luck.

PS - To get your XF fix, just steel Rick's when he's not looking.