If 12V compressor fridges are so efficient why do I need a big 100AH battery? It’s a question I see pop up fairly often. So today I’m going to do some comparisons between a tiny 4Ah battery like this… and a 100AH battery. F
first of all – when a compressor fridge turns on and starts to cool is when it draws the most current. When it’s already cold and the compressor is cycling on and off it’ll draw significantly less.

While your Adventure Kings 45L fridge may draw 3A while it’s running – it might only be on for 20 minutes of every hour, resulting in an average use of 1AH. This is all impacted by a couple of actions though, and your camping fridge will use less power if you can keep it cooler, that’s easy by keeping it in the shade – ensure it has good ventilation and use a fridge cover for extra insulation too. But what happens when you try and power a fridge on a small 4AH battery? you’ll find that the 12v fridge starts straight up and runs perfectly. The issue is, if you leave the compressor fridge running for about 20 minutes and we can see the fridge is now at 5°C. As a rough estimate, if the fridge is drawing 3 amps for 20 minutes you’ll have used about 1Ah or about 1/4 of the battery capacity already! So once the compressor fridge cycles on and off again the battery might only last another 20 minutes before it needs to be fully re-charged.

Next I’ll explain exactly why I always recommend adding solar to your setup, but why it’s important to also up-size your battery bank at the same time. Because the example above is such a scaled down setup let’s say we were running a small 20W solar panel into a PWM regulator to charge this AGM battery about 1.6Amps. That’s enough to cover the low power draw of a 12V compressor fridge, but only just. So at this rate it’ll keep the battery fully charged, but as soon as the sun goes away, the fridge will continue using power and the solar will never catch up. With only 4AH total capacity or 2AH usable capacity, once the sun goes down, at most you’ll have 2 hours of time that your 45L camping fridge will run… That’s why you need a larger battery. And in this case bigger is better. So next let’s use the same example of a small solar panel, but a larger camping battery!

A 100Ah battery will let you run an Adventure Kings 45L camping fridge like this for around 50 hours, assuming it’s drawing around 1AH on average. Of course that’s affected by temperature, how many times you open it and whether you add more items into the fridge that need to be cooled down. 50 hours is two full days and nights. But if you wanted to extend that you can connect your solar panel up from day one! Now so long as the sun is out, the battery is going to stay at 100% capacity. But again here’s the problem: Once the sun goes down your fridge is continuing to draw that small amount of power… let’s imagine the sun goes down at 6PM and wakes up again at 6AM, but you’re camped near a tree line and the sun doesn’t really hit your campsite until 8AM. By 8AM your fridge has used 14Ah of capacity, so when your little solar panel starts working again, you’re already down to 86Ah. In ideal conditions your solar panel will be able to supply enough to keep it at that level all day until the sun goes down again.

The next morning you wake up and your 100Ah battery is now down to 72AH. And this will continue for a couple days until you reach 50% capacity and really need to charge your battery back up. Now the next issue is that this situation is hypothetical – it’s implying you have ideal sun all day long and you’re pointing your solar directly at the sun for every minute of the day. In reality as the panel heats up, or isn’t directly facing the sun or even any time a cloud passes over, you’re losing your solar efficiency. It may not be enough to cover what the fridge is drawing and therefore your system suffers further. The only way to solve the issue is by stepping up to a larger battery and a more powerful solar panel. Running two 100AH batteries and a 160W Solar panel with a regulator would extend your camping time massively. But you still need to be aware that poor weather, not-ideal solar panel angle and panel temperature will affect solar output – plus the ambient temperature, what your fridge is set to, how many time you’re opening it and weather it’s copping any sun will affect how much power your fridge is using. Plus you might want to run more than just a camping fridge! So anytime you charge your phone or turn on a camp light you’re using more power that your solar has to add back in.


Jumping back to the 4AH battery, that’s much more of a problem because we’re already so close to the limit. And in that case it’s not as easy as throwing on a bigger solar panel – there’s still the obvious problems of not getting ideal conditions and the sun disappearing at the end of the day… plus you need to think about the charge rate of your 12V battery and how charging is affected by the state of charge of the battery. This 4AH battery has a maximum charge rate of 1.35A, while a 100Ah battery ideally can be charged at 25Amps… But in both cases, as the battery charges, the amps will drop down. This 100AH battery will only accept a 25A charge until it reaches its set voltage on the regulator – at which point the voltage will stay put, while the current drops off. This is another reason you need to oversize your solar! While it’s capable of putting out max power, a 12V battery will limit the amount of power coming in once it has reached maximum voltage. So if your solar can put out a maximum of 10A – consider that you’ll lose some power output in real world conditions. Let’s say it’s now at 8A, plus it’s a scorcher and you’re using your camping fridge more than usual… so it’s drawing 2Ah on average, next you’re also charging a phone or tablet from your battery, using about another A/h per hour You’re now only getting 5A from your solar panel.

If your battery is almost full, then running 5A is enough to keep it topped up – the battery probably can’t accept much more than that anyway with its state of charge. That means it’ll easily stay nice and charged overnight. If on the other hand your battery is already down to about 60 or 70% capacity, your 5A is now not so good! The battery can accept a much higher rate of charge so it’s going to take even longer to reach the maximum voltage. You may never fully charge up your battery in this situation. So – Yes an Adventure Kings camping fridge will run on a tiny battery and that’s testament to how efficient these are – but it won’t run for long due to the minimal capacity. Plus, you need to upsize your solar to take into account not only the weather and the real world, but also the properties of your battery and they way they charge!