Owning an RV or campervan, it’s common to have a 12 volt refrigerator to keep food fresh and/or frozen.
While the internal temperature is usually relative to the ambient outdoor temperature, a decent brand of refrigerator like Dometic can keep food and drinks cool enough in most seasons and locations.
It’s preferable to run the refrigerator on a 12-volt house battery system instead of relying on either a split relay or a DC-to-DC charging system.
Also, recharging by harnessing solar power avoids the need to run the engine and drive, or let the engine sit idle during a charging cycle.
It puts less of a toll on the starter engine, saves on gasoline or diesel fuel, and reduces wear & tear too.
How Long Will a 12 Volt Battery Run a Refrigerator?
How Long Will 12v Fridge Run on Battery
Naturally, you want to determine how long a refrigerator will run on the battery pack – a single 100-watt deep cycle battery or several connected within a battery pack.
The answer depends on various factors including the size of the fridge, its average power usage, the availability of power from the battery (or batteries), the battery type, and how much power can be drawn from them without causing potential damage.
Let’s look at an example…
How long will a 100ah battery run a fridge?
We’ll start with a simple example of a lead-acid battery. It’s a deep cycle variety, not a starter battery. So, it’ll supply power slowly rather than in a few larger bursts and won’t drain quickly.
A lead-acid deep cycle battery usually has a suggested depth of discharge of 50%.
What does this mean? It means that the battery can be safely discharged to half its maximum capacity.
After that point, it’ll supply power but risks permanently damaging the cells inside the battery.
To avoid destroying the battery sooner and needing to replace it, only discharge a lead-acid battery to 50% and then recharge from there.
As a side note, lithium or lithium-ion phosphate batteries allow up to 80% discharge; these batteries are coming down in price, but they’re still a premium option.
With lithium, perhaps 80ah from a 100ah lithium battery is accessible.
Running the 100ah Lead-Acid Battery Calculations
When a deep cycle battery has a 100ah (amp-hour) capacity, only half of that – 50ah – is safely usable.
A fridge will have suggested annual power consumption in its specifications and product manual. This is the approximate power usage. For example, a refrigerator may use 700kWh per year. This would be equivalent to 1.92kWh per day. That’s 80 watts per hour.
Battery capacity will vary but with a 100ah acid-lead battery, 50ah is usable.
Watt-hours are calculated next. The 50ah is multiplied by 12 volts. The result is 600 watts.
To calculate the hours of a refrigerator’s running time, the watts of the battery capacity are divided into the fridge’s hourly watts consumption rate. This is 600 watts divided by 80 watts. The answer is 7.5 hours for how long will a 100ah battery run a fridge?
Read Also: How to Tell If a Deep Cycle Battery is Bad
How Long Will Dometic Fridge Run on Battery?
There is nothing special about Dometic in terms of it tasking a 12 volt battery less than other brand
What does matter is how much food & drink storage capacity it offers and what its annual power consumption is.
Clearly, the larger the refrigerator that’s required in a campervan or RV, the more battery capacity will be needed to sustain it when off-grid or away from campground hook-ups.
Sometimes power information is difficult to locate. It also comes in different measurements like amp-hour (ah) usage for a fridge, freezer, or cooler, rather than annual usage.
Because of this, it’s often necessary to convert the figures to figure it all out.
We’ll use the neat Dometic CFX3 45-liter Portable Refrigerator and Freezer as an example.
It is a popular type, especially for van lifers who wish to slide it under a raised platform bed or below a kitchen worktop. It has a top lid that opens upward, with digital controls at the front, and a handle to slide it out.
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Running the Calculations For a 100ah Lithium Battery
The specifications suggest around 52 watts per hour of usage when the refrigerator is first cooling down to the required temperature.
Power usage is then reduced to as low as 2 watts to maintain that temperature. That is until the lid is lifted and warmer air is let inside.
Therefore, the average power requirements are likely around 30 watts average over several hours of continuous usage.
Using the Dometic CFX3 powered by a 100ah lithium-ion battery this time, it’s possible to discharge 80% safely for the maximum recharge cycles. Therefore, 80ah of the battery capacity can be safely used to power this fridge.
Watt-hours are calculated as 80ah multiplied by 12 volts. The result is 960 watts.
Therefore, how long will an RV fridge run on battery? For the Dometic CFX3 45-liter model, the calculation of 960 watts divided by 30 watts indicates it’ll provide 32 hours of reliable operation.
Read Also: How Many Watts Does a RV Refrigerator Use?
Running RV Fridge on Inverter?
It’s possible to use either a three-way refrigerator that accepts 120-volt electrical inputs or a residential fridge in an RV via an inverter.
Running an RV fridge on an inverter requires more power because around 10 percent is lost during the conversion process.
The inverter will magically convert the 12-volt battery power to 120-volts. Then it is usable for American household appliances, including a fridge.
Read Also: Should I Leave My RV Refrigerator On all the Time?
How Many Batteries to Run a Refrigerator?
When running a fridge off a battery and looking at the above examples for both lead-acid and lithium-ion batteries, it provides some pause for thought.
Clearly, the type and number of batteries play an important role in RVing or Van Life. Â
Multiple batteries provide a greater total power capacity to keep a refrigerator running for longer.
It’s important to consider whether an investment in Lithium or LiFEP04 batteries will be worth it. For sure, their highest safe discharge, of at least 80%, can stretch out the hours a fridge can run for.
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If lead-acid or another non-lithium battery is already onboard, you may wish to add a second battery to create a battery bank.
It should match the existing battery type and capacity to effectively double the runtime.
Therefore, how many batteries are needed to run a refrigerator depends on your allowable battery power capacity and how power-hungry your refrigerator is.
Furthermore, given that other appliances might need to tap into the 12-volt battery supply too, do consider all the power consumption requirements. Not just for the refrigerator!
What Size Battery to Run Fridge?
The 100ah or 110ah is popular across different battery types.
There are larger-capacity batteries, but it’s worth thinking about the ability to recharge them once they get near the safe discharge level.
A battery may have a higher total capacity, yet the ability to fully recharge it may not be available.
Due to a desire to drive less when recharging the battery or because your solar power solution isn’t installed yet, multiple lower-capacity batteries might be preferable over one larger one.
Also, with a dual or triple 12-volt battery bank setup, should one battery fail, it can be bypassed until a replacement can be purchased.
A single, larger capacity deep cycle battery is a single point of failure for someone enjoying van life or their RV. As such, we’d opt for smaller 100ah-ish capacity batteries.
They also tend to take up less floor space too.
Read Also: How to Keep RV Fridge Cold While Driving?
Closing Thoughts
The subject of batteries and appliances can seem complicated for people new to #vanlife or the RV lifestyle.
However, it’s just a case of getting your facts straight and running the numbers. Then you can see how much life you can get out of a refrigerator or a cooler before the battery is overtasked.
Overall, Lithium is a better option due to the higher usable amp-hour capacity per battery. Also, owning multiple deep-cycle batteries is better than relying on one alone.
Nevertheless, many people begin with one setup and gradually build or upgrade to something better. This happens because it takes time to reach a greater understanding of their power needs.
Also, this may include purchasing a power station or a generator, adding solar panels on the roof, and other power solutions besides deep cycle batteries alone.
