Compressor, absorption and icebox: how the three compare

Three kinds of portable cooler turn up in camping shops. They cool in very different ways, and that decides how much battery each one eats.

Icebox (cooler box)

• How it cools. Ice melts and soaks up heat. No power needed.
• What it costs in space. Dometic says that in a normal ice chest you need to fill it with roughly 50% ice¹.
  • That's half your storage gone before you add food.
• What it costs in hassle. ARB lists the usual problems: stops to buy ice, food spoiled by melted ice, and ice taking up half the room².
• Power cost. Zero. Everything else is a trade.

An icebox suits short trips. It needs no wiring, so none of the electrical safety points below apply.

Absorption fridge

• How it cools. It uses a heat source to provide the energy that drives the cooling³.
• Moving parts. None. An absorption refrigerator has no moving parts and runs almost silently³.
• Where it fits. Wikipedia describes it as an alternative to compressor refrigerators where electricity is unreliable, costly, or unavailable³.
• Noise. Dometic calls the absorption type "absolutely silent"¹.
• Power cost on 12V. High. In Dometic's own example, an 85 watt absorption unit on 12 volts works out to 7 Ah an hour, or 168 Ah a day¹.
• Efficiency. Its quiet running came at a price. Wikipedia says the advantage was eroded by much poorer efficiency than compression fridges³.

Dometic lists the absorption type as running on 12 volts, 230 volts or gas¹. This site doesn't cover running gas appliances. Follow the maker's manual for ventilation and fitting, and use a licensed gas fitter if you're unsure. Never run gas appliances, or generators, inside a tent, van or any enclosed space, because of the carbon monoxide risk.

Compressor fridge

• How it cools. An electric compressor. It runs, then rests.
• Noise. Dometic describes an occasional, quiet running noise¹.
• Power cost on 12V. Much lower in Dometic's example. A 48 W unit at 3.75 A, running about 22 percent of the time, comes to under 1 Ah an hour¹.
• Maker's view on long trips. Dometic says longer periods of use, for example more than 2 days, call for compressor technology¹. That's the maker's opinion, so weigh it.

Side by side

Be careful reading the table. The absorption and compressor examples are two different Dometic models of different sizes. They show the pattern, not a like-for-like test. Dometic's own figures also assume particular conditions, so your numbers will differ.

Which suits off-grid use

• Long stays with no mains: a compressor unit draws far less battery power than the absorption example above. Check it against your own battery on the runtime page.
• Gas available and silence wanted: an absorption unit is an option, if you follow the safety rules above.
• Weekend trips close to shops: an icebox may do the job.

Fitting a fridge to a battery? Isolate the battery before any cable comes off or goes on, and work from the maker's instructions. A licensed auto electrician is the right call if you hesitate. Permanent mains wiring is licensed work in Australia.

The rest of this site looks at compressor fridges, since they're the ones people run off a battery day after day. Start with what a fridge really uses. That page has numbers from Dometic's CFX3 100¹.