What functions do I need?
The more functions a 12 Volt cooler has, the more expensive it is. The most basic are just coolers: they will keep contents cold but not frozen. Some coolers also come with a warming function: this will be warm enough to make your food or drinks hot, but it will not get hot enough to actually cook the food. (Please note that this temperature is ideal for keeping hot foods hot, but it is also in the ideal growth range for bacteria, so please exercise caution and common sense when transporting food. The warmer is not recommended for food storage exceeding 45 minutes at a time.) A portable fridge/freezer will keep the contents cold or even keep them frozen: you decide what level of cooling you need and set it accordingly.

What capacity do I need?
The capacity of 12 Volt coolers is usually measured in quarts. In order to give you a better idea of how much this is, often the capacity in 12 ounce cans is also given. On average, 1 quart can hold .75 (not quite 1) can. So, a 12 quart cooler could hold around 9 cans. The actual dimensions of the cooler can also give you an idea if favorite containers can easily fit inside.

Can I plug a 12 volt appliance into my wall socket?
12 Volt DC appliances can be converted to work in an ordinary 110 Volt AC wall socket like those in your home. Some 12 Volt coolers come with the AC adaptor, but for some it is sold separately. Be sure and read the description and specs carefully to determine which is true for a particular cooler.

Can I set the exact temperature of my 12 Volt cooler?
The 12 Volt coolers will hold a fairly constant temperature, but you can not set this temperature exactly, only adjust it to be cooler or warmer than it is. Also, be aware that every cooler will be affected by the ambient temperature: the cooler the temperature it is in, the colder it will be able to stay. For example, some of the coolers do not give a specific temperature as their minimum able to be reached, but will say something like "40 degrees below ambient." This means that if you keep the cooler in an air conditioned house set at 75 degrees, the inside of the cooler can get as low as 35 degrees. However, if the cooler is outside in 90 degree weather, the inside will only get as low as 50 degrees. The fridge/freezers are more powerful than the standard coolers and can reach much lower temperatures in the same ambient temperature because they use compressor cooling rather than thermoelectric cooling.

If I plug a 12 Volt cooler into my car, will it work if my engine isn't running?
A 12 Volt cooler will continue cooling when your engine is off if your car powers the cigarette lighter socket when the engine is off. Some cars do, some cars don't. If your car does power the cigarette lighter socket when the car is turned off, the cooler will likely run for about 2-3 hours. However, the worst case scenario is that the cooler will only run for a few minutes. The best case scenario has the cooler running overnight with no problems. Factors affecting best/worst case scenarios range from the age of your battery, the number of other things your battery is powering at the same time (lights, etc.), the size of your battery, and more.

How long will a 12 Volt cooler keeps its contents cool if it is not connected to a power source?
This depends on conditions such as the ambient temperature, how full the cooler is, and if you open the lid. 12 Volt coolers are well insulated and should keep their contents cool for a few hours in the absence of electricity, under ideal conditions.