DC voltage drop.

I know you are all dying to know the outcome.

We managed to continue with our trip but were parsimonious with the battery use, as much as we could be, and the DC voltage was still reading just under 12v when we got home. Our service engineer checked the whole system out and it was a defunct charger unit in the PDU. That is now replaced, and the battery is fine too, thankfully. So now ready for the off again.