The simplest and cheapest option for portable cooling, passive coolers use reusable freezer packs which you freeze at home before your journey to keep the contents of your cool box chilled. Campsites often have freezers for refreezing the blocks and Camperlands recommends having 2 sets of blocks; one for use in your cool box while the other set is refreezing to ensure constant cooling performance.
Passive coolers are the cheapest option and are recommended for use on picnics and short trips away and can double as food or drinks coolers for BBQs or parties at home.
Although powered coolboxes often have both 12V and 240 volt power supply options, the 12V option is mainly intended for use when traveling due to the ampage draw on the 12V supply. Thermo-electric coolboxes will keep run from a vehicle 12V supply while the motor is running without draining the battery and are sufficiently insulated to keep things cool if you stop at a service station on your journey. They can however drain your car battery if left running when the motor is switched off (look out for coolers with a battery safe mode which cuts off before the battery gets too low).
Thermo-electric coolboxes are usually recommended for UK use where a 240V supply is available on site through your vehicle connection or an independent mobile mains kit sometimes referred to as a EHU. Electric cool boxes generally have a cooling capacity of around 18 to 20 °C below ambient temperature and some also have a warming function for hot food stuffs.
Cheaper than a genuine fridge, electric coolboxes are recommended for picnics or cold drinks on long journeys or UK campsite use to chill basic foodstuffs where a mains electric supply is available.
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Absorption fridges are similar to the compression fridge you may have at home, but they run much quieter so as not to disturb your nights sleep. They can generally be run from both 12v and 24 volt electric supplies as well as gas giving you the freedom to use them where a mains electric supply is not available or simply unreliable.
Absorption fridges will generally achieve a temperature drop of around 25 to 30°C below ambient making them suitable for use in hotter climbs as well as the UK. Many will have variable performance to prevent over chilling in colder months of the year. Although they are more expensive than electric coolboxes, with no moving parts absorption fridges tend to have a longer lifetime than powered coolboxes.
Recommended for use in both the UK and Europe where higher performance may be required or where mains electric supply can't be relied upon so gas power option is an advantage.
Compressor units are more powerful than the other types available enabling them to achieve a greater temperature drop and are often capable of being used as a freezer. However, because this unit type is more powerful it runs from mains electrics only.