Something like this..
Those are not a compressor fridge, they are based on a solid state device based on the "Peltier effect" of passing a current through a semi conductor which creates a cold side and a hot side.
They are horribly inefficient electric wise and they can only cool down to 40 degrees below the ambient air temperature.
Basically if it is 80F the lowest it can get inside is 40F which is marginally OK for food.
If it is 90F then the lowest it can get inside is 50F which is in the danger zone for food.
If it is 70F the lowest it can go is 30F and then your food starts freezing..
In a nutshell, no real reliable temperature regulation..
There are much better 12V fridges out there which have a compressor, yes they are not cheap but they are far more reliable as far as keeping your food cold..