Joseph Baz replied:

Andrew,like all electric appliances there is a lot of variables,i have a 550cca battery fitted to my camping trailer,it gets charged via the auxiliary cable in the trailer plug,with a full battery on the fridge setting and two fluoros
i get about 30 hours under a shady spot but if a lot of sunshine gets on the fridge it gets cut down to less than 20hours,if you read trough you may find that all the claims are made under optimun conditions.
Cheers
Joe

Ian replied:

The other thing is that the 1 setting power draw is an average, the fridge will draw its usual current (probably around 3-4 amps) but being a warmer setting, the compressor will run less (cycle time). This is also dependent on the conditions, and for this you need test conditions to match those that the specs are quoted at.

As an example, if 1 Amp is quoted for 20oC, if it is say 32oC, much more power will be used.

In short, every situation is different, and 24 Amp hours used in 12 hours in reality is probably fair. I do not own an engel, but I use a custom built fridge with a Danfoss compressor that would use similar power.