There are lots of reasons to need a portable fridge. Whether you're camping or in the car, these can be an absolute necessity. Portable fridges range in size between 10 to 100 litres.
There are a few things to consider when choosing a portable fridge. Weight is a consideration if you're planning to carry the fridge around by hand. Volume is also important, the larger a fridge is the more power it consumes and the more it will weigh. However, having more cool items in the fridge will keep the contents cooler for a longer period of time. Another major consideration is the longevity of the portable fridge's power source.
There are three types of portable fridge: thermoelectric, compressor and gas. Thermoelectric fridges are powered electronically, and they're always on. They can only really be used to sustain their contents temperature. So you can't expect to make ice cream and freeze ice cubes with a thermo electric portable fridge. These are powered electronically, so they can be used in a car.
The second style of portable fridge uses a compressor to keep its contents cool. These work like regular refrigerators in the kitchen; they only turn on periodically. They're also capable of keeping things much cooler for longer than thermo electric. In addition to that, they draw less power, so they can last longer. The down side to compressor fridges is that they cost more and weigh more than thermoelectric fridges. However, if you're going camping or planning to use your fridge for a longer period of time, a compressor style portable fridge may be best for you.
Gas fridges don't need a power source to run, they can last the longest in isolated areas. Their downside is that they're more expensive than the electric fridges. They also cannot be operated in enclosed areas. Obviously using the gas fridge in a car is out of the question, but using the fridge inside of a tent can also lead to carbon monoxide poisoning.