Thanks chaps. Will take a look for that button.

If using freezer blocks, put them on the top shelf not in the bottom of the fridge & don't leave ice cubes in the freezer, chuck them out & make new ones when you arrive....!

What's probably more pertinent Roger is how it was after 9 hours without power as by the time you got home the drive from the post could have chilled things down again.

I have seen an electrical hookup on a cross channel ferry, can't remember which one; it was being used by a private funeral vehicle repatriating a coffin.
However, we forgot to turnm the fridge off on the longish ferry crossing from Oban to Barra, the crew were obviously used to it as before the bow door was fully open they wheeled a power truck up and got me started. We were advised to drive right around the island to recharge the car battery, it took all of about 20 minutes !

We didn't turn the fridge off when on our 30 hour ferry ride. I just assumed that when the ignition is off, the wiring pin that powers the fridge from the car battery is not live. Maybe that's one of the advantages (or disadvantages) of having vehicle specific (dedicated) wiring for towing.