My experience with fridges......
I own a 7-8 year old 74lt Evakool from new and a second hand 47 lt evakool
Keep them in the shade, duhhh, I have had a mate ( not to bright) complain his fridge was using heaps of power, he had it next to him in the qld sun,38 deg day trying to keep the kids iceypoles frozen?....
Pack them cold, I even pack them frozen, If I am running the unit as a fridge I will put the meat in the unit frozen. Don't pack everything in warm then try to chill it at camp
Pack them full, empty fridges run more often
Keep out of them, keep the kiddies grubby hands out of the fridge every five seconds
When I do this I have never ran out of battery power, I have 2 x 95amp hr batteries, but but but no two trips have every been the same, different food, different weather, different everything so it's so hard to say the fridge runs at ..... Amps, it's relative
All I can say is got my second hand 47 lt fridge was cheap because is was not running right, probably 10 year old fridge, I bought it on a punt, got it home, opened up the compressed box, cleaned the layer of dust off the condenser fins, runs like new.
Buy something someone else has tested for you, evakool are great, I have heard engel run forever, I would hate to spend $600 to test a product that your then not happy with