So, you have a 12 Volt battery, a refrigerator, and you’re wondering “how long will the battery run the refrigerator?”
Due to the many factors involved (temperature, usage, age of the refrigerator, etc..), there are no general or 100% accurate answers to this question.
However, you can still get a pretty accurate estimate. All you need are 2 pieces of information that are available to you:
- The energy consumption of the refrigerator.
- The available capacity of the battery.
In this article, I’ll provide some estimates and show you how you can do it yourself. I’ll also explain a few things that you might need to know.
How long will a 12 Volt battery run a refrigerator?
In general, a 12V-50Ah battery can run a 2 cubic feet 12V fridge for 35 to 50 hours before it’s completely depleted. A 10 cubic feet RV refrigerator can run on the same battery for only 10 to 15 hours.
However, it’s important to note that:
- Batteries should not be fully discharged.
- Different battery chemistries have different acceptable depths of discharge (DoD).
For example, a 100Ah Lead-acid battery can only supply about 50 Ah of energy without reducing battery life. While a 100Ah lithium battery can supply 80Ah.
The table below gives you an idea about how long you can run different types and sizes of refrigerators without damaging the battery:
|Fridge type||Fridge Size||Lithium Battery||Lead-Acid Battery|
|12V Fridge||2 Cu. ft.||28 to 40 hours||55 to 80 hours||18 to 24 hours||36 to 50 hours|
|Mini-fridge||4 Cu. ft.||16 to 20 hours||32 to 40 hours||10 to 14 hours||20 to 28 hours|
|RV fridge||10 Cu. ft||10 to 12 hours||20 to 24 hours||6 to 8 hours||12 to 16 hours|
|Full-size fridge||18 Cu. ft.||6 to 8 hours||12 to 16 hours||4 to 5 hours||8 to 10 hours|
To estimate how long a refrigerator would be able to run on a 12v battery, divide the battery’s usable capacity (Ah) by the refrigerator’s estimated hourly energy consumption (Ah):
Refrigerator Run Time (hours) = Usable Battery Capacity (Amp-hours) ÷ Refrigerator energy consumption per hour (Ah/hour)
Available Battery capacity:
When a battery is fully discharged, it will have fewer charge/discharge cycles, and its overall capacity is at risk of being reduced.
So when trying to determine how long your battery will run your refrigerator, consider the life and longevity of the battery itself.
Here are a few battery chemistries and their optimal depth of discharge (DoD):
|Battery Chemistry||Recommended Depth of Discharge (DoD)||Usable Battery Capacity|
|FLA (Flood Lead-Acid)||50%||25Ah||50Ah|
|SLA (Sealed Lead-Acid)||50%||25Ah||50Ah|
|AGM (Absorbed Glass Matt)||50%||25Ah||50Ah|
|Li-Ion (Lithium Ion)||80%||40Ah||80Ah|
|LiFePO4 (Lithium Iron Phosphate)||80%||40Ah||80Ah|
For example, if you have a 50Ah lead-acid battery, the usable capacity of the battery is only 25Ah.
Refrigerator’s hourly energy consumption:
A refrigerator’s energy consumption can’t be determined as precisely as many other electrical appliances. This is because the compressor – which is the main electrical component of a fridge – has running cycles, i.e., duty cycles.
This means that although a fridge is plugged in all the time, it turns on and off in a more or less random way throughout the day.
However, as a general rule of thumb, the average refrigerator only runs for about 20 mins every hour.
Therefore, if you know the amperage of your refrigerator, you can simply divide it by 3 and you get the average hourly energy consumption in Ah (Amp-hours).
If you have the wattage of your refrigerator, divide it by 3 and you get the average hourly energy consumption in Wh (Watt-hours). Then divide those watt-hours (Wh) by the voltage of the refrigerator to get the hourly energy consumption in Amp-hours (Ah).
Consider the following example.
How fast will a 12 Volt cooler discharge your battery?
The average 12V fridge (1.6 to 2.5 Cubic feet) uses about 1.3 Ah of energy per hour. At this rate of energy usage, a 12V-100Ah battery can power a 12V fridge for about 3 days before the battery is completely discharged.
Here’s an example:
The manufacturer of this 1.6 cubic feet Euhomy 12V Refrigerator specifies 45 Watts as the power usage.
As a general rule of thumb, this 12V fridge should be expected to consume about 15Wh of energy per hour. At 12 Volts, this energy consumption translates to 1.25Ah per hour.
Now, let’s say I want to run this fridge on this 12V-100Ah LiFePO4 Ampere Time battery.
We know that the recommended depth of discharge for a Lithium Iron Phosphate battery is 80%, so the usable capacity of this battery is 80Ah.
Now let’s estimate how long this 12V fridge would be able to run on the battery without damaging it.
Refrigerator Run Time (hours) = Usable Battery Capacity ÷ Refrigerator energy consumption per hour
Refrigerator Run Time (hours) = 80 Ah ÷ 1.25 Ah/hour
Refrigerator Run Time (hours) = 64 hours
Theoretically, our fridge would be able to run for 64 hours on this battery.
A typical 12V-50Ah battery could run a portable 12V refrigerator (2 Cu. ft) for one day and still have about a third to half of its capacity. However, bigger refrigerators would require a much bigger battery bank.
For example, a standard residential RV fridge (10 Cu. ft.) would need around 1000Wh (Watt-hours) per day to run. Which is equivalent to about 90Ah at 12 volts.
As mentioned in the sections above, the battery bank should be sized to supply energy to the refrigerator without exceeding a certain depth of discharge (80% for lithium batteries and 50% for lead-acid batteries).
The table below shows different refrigerator sizes, their estimated daily energy consumption, and how much battery capacity it would take to run them for 1 and 2 days:
|Fridge type||Fridge Size||Daily Energy Consumption||Lithium Battery||Lead-Acid Battery|
|1 Day||2 Days||1 Day||2 Days|
|12V Fridge||2 Cu. ft.||350Wh||40Ah||80Ah||60Ah||120Ah|
|Mini-fridge||4 Cu. ft.||600Wh||60Ah||120Ah||100Ah||200Ah|
|RV fridge||10 Cu. ft||1000Wh||120Ah||230Ah||180Ah||360Ah|
|Full-size fridge||18 Cu. ft.||1500Wh||200Ah||400Ah||300Ah||600Ah|
Note that the table uses 50% DoD (depth of discharge) for lead-acid batteries and 80% for lithium batteries.
How to size a battery bank for a refrigerator?
If you want to determine how big of a battery bank you need to run a refrigerator, you need 3 pieces of information:
- The refrigerator’s estimated daily energy consumption.
- The number of days you want to run the refrigerator.
- The chemistry of the battery you’re going to use.
According to the manufacturer, this Dometic 12V fridge consumes 1.5Ah/h (1.5 amp-hours per hour).
Let’s say I’m going camping for 3 days and I’m going to use lithium batteries to power it during my trip.
3 days energy consumption (Ah) = 1.5 Ah/hour x 72 hours
3 days energy consumption (Ah) = 108 Ah
During these 3 days, the refrigerator is expected to consume around 108Ah at 12 Volts.
Since I’m going to use a lithium battery bank, I only have access to 80% of the battery’s capacity. The total capacity of the battery bank can be calculated as such:
Battery Bank Capacity (Ah) = 108 Ah ÷ (80/100)
Battery Bank Capacity (Ah) = 135 Ah
This means that the lithium battery bank I need would have to be rated at 135 Ah or more.
If you have a bigger refrigerator, it would probably make more sense to use solar energy. For more information about that, click here or go to the section below.
How to make the battery last longer?
There are a few things that you can do to preserve energy and potentially extend the usage time of the refrigerator:
Shade and insulation:
Insulation materials are a simple and cheap way to increase battery longevity and protect your refrigerator.
When a refrigerator is placed under direct sunlight, not only will it consume way more energy, but it will also be at risk of failing due to the excessive workload.
If your refrigerator is going to be sunlit, make sure to use a reflective insulation shield.
Cool the fridge down before plugging it into the battery:
Refrigerators need a lot of energy to initially cool down. The battery would last longer if it’s only maintaining the low temperature inside the refrigerator rather than supplying the energy needed to create it.
Most 12V fridges have a 120/220 VAC plug, so if you’re planning on running one on batteries, consider plugging it into the wall and cooling it down at home.
How much clearance around the fridge?
Refrigerators cool down the air inside by performing a temperature exchange with the outside environment. For this to happen, a certain amount of airflow is required.
If the fridge is surrounded by stuff, there won’t be much airflow.
So make sure to leave at least 2 inches of clearance on each side of the fridge, especially the part from which the heat dissipates into the air (generally located at the rear of the refrigerator.
Fill up your fridge
It might sound counter-intuitive, but empty fridges consume more energy than fuller ones.
This is because it takes more energy to keep the air cold, than it takes to keep the food cold. Especially if the fridge is frequently opened.
So, make sure to take advantage of the cubic footage of your refrigerator.
Consider using solar power:
Let’s say you’re going camping for a couple of days and have a battery that can run your fridge for 1 day only.
It’s much cheaper to buy a solar panel than to double the size of your battery. Plus, a solar panel/battery combo can potentially run your refrigerator forever.
This brings us to the next section.
To run a small 12V refrigerator (2 Cu. ft.) on solar power, you would need a 100W solar panel and a 12V-50Ah battery. For a bigger refrigerator such as an RV fridge (10Cu. ft.), you would need 200 to 300 watts of solar power and 120 to 180 Ah of battery capacity.
However, you also need a solar charge controller, and in case you have a refrigerator that only works on AC, you’ll also need an inverter.
For more information, please refer to this article: How many solar panels do you need to power a refrigerator?