Small Fridge

At that price it would be one of those peltier effect coolers. Not really a 'fridge' which usually has a compressor.
These coolers can only achieve a certain temperature difference (around 40 degrees C unlerss its a really fancy design with cascaded peltier elements) between outside and inside the fridge. So, if you park your car in the sun, the inside of the car easily gets to 50 degrees and your poor cooler struggles to maintain +10 degrees within.
I would not recommend to leave it connected when stopping for some time. These coolers run virtually all the time and, though their power consumption is not particularly high, it all adds up.
You really get what you pay for, used car fridges go for a lot more than $99.-
Klaus

I purchased a WAECO version of these, cost $89, only used for long trips to keep cold drinks cool, will not actually cool drinks unless you have several days to spare, and then only to 8 - 10 Celcius. O.K. when travelling with aircon on if hot, but as above, you get what you pay for, just remember to make sure the drinks are cold before putting them in.
Rolande

I used to have a Waeco one of these and it could only get the inside about 20 degrees cooler than outside while drawing 5 amps continuously - not much use in the tropics.

Traded up to a compressor fridge (I got an EvaKool as it has the best insulation for the size/weight) and it draws about 1.5 amps average and stays at 2 degrees inside, even when parked in the sun in a western queensland summer.