Bongo Fury

We spent the weekend at a very hot Gurston Down hillclimb in our Freda but by Saturday afternoon the fridge had stopped working (it's a small Waeco toploader - can't remember if it's a CB-36 or a CB-40).
Normally the battery (a recent Energy Bull 80 Ah) easily lasts for a weekend away so I'm surprised it stopped this weekend. Starting the van enabled the fridge to start but without the engine running the fridge remained off. The instructions suggest some possible causes, 2 of which seem most likely:
1) Battery voltage too low or 2) Ambient temperature too high
1) is possible if the fridge were running for much longer because of the high ambient temperature but I still think it unlikely unless we had left something else on that drained the battery (we checked and don't think so).
2) is possible as the rear of the van was facing south (it's an end conversion) and there isn't a great deal of ventilation around the fridge. The manual says it should work at up to 55 deg C - is it possible it got that hot? N.B we always turn the fridge off at night as it's right by our heads so we wouldn't know if it worked later when the temperature had dropped but it didn't fire up Sunday morning so I guess not.

Has anyone had a similar problem and if so did you find the cause? Anybody else got thoughts on the cause and what we could do to prevent it happening again?
I have thought about getting a battery voltmeter fitted so I can see the state of the leisure battery.

Check and clean all the electrical connections, fuses, switches etc. that may well be the problem, if you have a meter then check the voltage at the fridge itself and watch what happens when it tries to turn on, quite often the voltage will drop below the allowed voltage hence it trips out, in which case check again at the battery and if there is a difference of more than about 0.5 volt check the connections as above, if the voltage at the battery terminals is falling much below 11 volts then it would indicate a badly discharged battery / faulty battery.

55 degrees c is very very hot. Bear in mind 30 is a very hot uk summer day in the shade. Put it this way, if you put your hand on your fridge where the warm bit is on the outside, and it was 55 c you would find it very uncomfortable.

The temperature in your van will make a big difference to battery performance of your fridge. A fridge takes the warm air inside itself, and exhales it outside itself, leaving less warm air inside (cooler!) and the warm air it removed outside. If your van is not ventilated then the fridge is fighting an uphill battle. All the warem air it is removing frm the inside is now warming up the fridge from the outside....

It does however sound like your battery is failing. My mate's bongo was the same. His 100ah battery gave hime almost three days of fridge power, but by the time i got to use it it would not last more than half a day. He had repeatedly run his battery flat, which kills its performance in short order.