To run a refrigerator on batteries for 24 hours, you would need anywhere from 50Ah to 300Ah (Amp-hours) of battery capacity. 50Ah being for a small 12-volt fridge/freezer (1.6-2.5 Cu. ft.), and 300 Ah being for a full-size refrigerator (18-22 Cu. ft.).
The right amount of battery capacity that you need depends mainly on these two factors:
- The refrigerator’s energy consumption.
- The chemistry of the battery.
In this article, I’ll show you how you can use these factors to calculate the right amount of battery capacity needed for your refrigerator.
I will also go into why you should consider solar energy and how you can size a solar system for your refrigerator.
How many batteries to run a refrigerator?
The table below shows the estimated capacity of the battery bank needed to run different types and sizes of refrigerators for one day:
Fridge type | Fridge Size | Daily Energy Consumption | Battery Chemistry | |
Lithium Battery | Lead-Acid Battery | |||
12V Fridge | 2 Cu. ft. | 350Wh | 40Ah | 60Ah |
Mini-fridge | 4 Cu. ft. | 600Wh | 60Ah | 100Ah |
RV fridge | 10 Cu. ft | 1000Wh | 120Ah | 180Ah |
Full-size fridge | 18 Cu. ft. | 1500Wh | 200Ah | 300Ah |
Notice that the table includes 2 battery chemistries, and the battery capacity is different for each chemistry.
This difference in the capacity needed is due to the difference in the recommended depth of discharge (or DoD for short) between the 2 battery chemistries.
Let’s take the 12V fridge as an example:
On average, a 12V car fridge consumes about 350Wh (Watt-hours) per day. In Amp-hours, it consumes about 30Ah per day.
This means that the battery would need to supply 30Ah of energy to power this refrigerator.
However, the battery should be able to supply the energy needed AND still maintain a certain state of charge.
This is due to the fact that fully discharging a battery will shorten its life and reduce its capacity.
Here are a few battery chemistries and their recommended depth of discharge (DoD):
Battery Chemistry | Recommended Depth of Discharge (DoD) | Usable Battery Capacity | |
50Ah | 100Ah | ||
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 |
In general:
- Lithium batteries can be safely discharged to about 20% (the recommended depth of discharge is 80%).
- Lead-Acid batteries can be safely discharged to about 50%.
This means that if we use a lithium battery for this fridge, its capacity would have to be about 36.5Ah (30Ah ÷ 0.8).
If we use a lead-acid battery, its capacity would have to be 60Ah (30Ah ÷ 0.5).
Also, keep in mind that the table is for newer and more energy-efficient refrigerators, older refrigerators may consume way more energy.
For instance, I have seen an example of an old 10 cubic feet RV refrigerator that consumes up to 4kWh per day, which is just too much.
To determine precisely how many batteries are needed to run your refrigerator, you need to answer these 3 questions:
- How much energy does your refrigerator consume per day?
- How many days do you want to run the refrigerator on the battery?
- What type of battery are you going to use?
How much energy does your refrigerator consume?
With most new refrigerators, you can easily figure out the daily energy consumption by referring to the EnergyGuide label.
For example, the following image shows the estimated yearly energy consumption of a 4.5 cubic feet mini-fridge.
If we divide 237 kWh (the yearly energy consumption) by 356, we get 660 Wh as the estimated daily energy consumption.
What if there is no EnergyGuide label on my fridge?
If the label is not available, you can estimate the energy consumption by using the wattage or voltage/amperage specified by the manufacturer.
For example, below is the specification label of a Whirlpool refrigerator:
On the label, the manufacturer specifies that the refrigerator uses 100 Watts of power (not to confuse with energy).
If the manufacturer does not directly specify the wattage, it can still be calculated:
Electrical Power (Watts) = Voltage (Volts) x Current (Amps)
For this example:
Electrical Power (Watts) = 220 V x 0.45 A
Electrical Power (Watts) = 99 Watts
Now that we know how much power this refrigerator uses, how can we estimate its daily energy consumption?
On average, refrigerators have a duty cycle of 33%. This means that for every 24 hours, a refrigerator only needs to run for about 8 hours.
So if you know the wattage of your refrigerator, its estimated daily energy consumption can be calculated as such:
Daily Energy Consumption (Watt-hours) = Wattage (Watts) x 8 hours
Daily Energy Consumption (Watt-hours) = 100 Watts x 8 hours
Daily Energy Consumption (Watt-hours) = 800 Wh
Now let’s see how we can use this information to calculate the needed battery capacity.
How to calculate the battery capacity needed to run a refrigerator:
To determine the battery capacity needed to run a refrigerator, multiply the refrigerator’s daily energy consumption (Wh) by the number of days for which it’s going to run on the batteries, then divide the result by 0.8 for lithium batteries, or by 0.5 for lead-acid batteries.
This will give you the battery capacity in Wh (Watt-hours). To determine the capacity in Ah (Amp-hours), simply divide by 12 (a single battery’s voltage).
Confusing? Here are 2 examples:
Example 1:
I have a small 12 Volt car fridge/freezer that consumes around 450Wh per day.
Let’s say I’m going camping for 2 days and I’m looking for the right size LiFePO4 battery (Lithium) to power my fridge:
Battery Capacity (Watt-hours) = Energy needed ÷ 0.8
Battery Capacity (Watt-hours) = (450Wh x 2) ÷ 0.8
Battery Capacity (Watt-hours) = 1125 Wh
To get the battery capacity in Amp-hours, I’ll divide this result by 12:
Battery Capacity (Amp-hours) = 1125 Wh ÷ 12
Battery Capacity (Amp-hours) = 93.75 Ah
A good fit would be this 12V-100Ah Ampere-Time lithium battery.
Example 2:
Let’s consider the example of a refrigerator that consumes 800Wh per day.
If I want to run this fridge for 3 days using AGM batteries (Lead-Acid), the capacity of the battery bank needed can be calculated as such:
Battery Capacity (Watt-hours) = Energy needed ÷ 0.5
Battery Capacity (Watt-hours) = (800Wh x 3) ÷ 0.5
Battery Capacity (Watt-hours) = 4800 Wh
To get the battery capacity in Amp-hours, I’ll divide this result by 12:
Battery Capacity (Amp-hours) = 4800 Wh ÷ 12
Battery Capacity (Amp-hours) = 400 Ah
So, the battery bank has to be rated at 400 Ah (At 12 volts).
4 of these Renogy 12V-100Ah AGM batteries would do a great job.
Please Note: If your refrigerator uses AC power, you’ll need to account for the efficiency of the inverter (85% on average). You can do that by dividing the calculated capacity by 0.85.
If you’re thinking about running the fridge only on battery for 2 days or more, and you’re thinking about buying the battery, it might be cheaper to use solar power.
If you have a solar panel and a battery, with enough sunlight, you could potentially run the fridge for free and for as many days as you want.
This brings us to the next section.
How much solar power do I need to run a refrigerator?
To run a refrigerator on solar energy, you would need anywhere from 100 Watts to 500 Watts of solar panels.
The table below shows different sizes of refrigerators, their average daily power consumption, how much battery capacity and solar power it would require to run them:
Fridge type | Fridge Size | Daily Energy Consumption | Battery Chemistry | Solar Power Needed | |
Lithium Battery | Lead-Acid Battery | ||||
12V Fridge | 2 Cu. ft. | 350Wh | 40Ah | 60Ah | 50-100 Watts |
Mini-fridge | 4 Cu. ft. | 600Wh | 60Ah | 100Ah | 100-200 Watts |
RV fridge | 10 Cu. ft | 1000Wh | 120Ah | 180Ah | 150-300 Watts |
Full-size fridge | 18 Cu. ft. | 1500Wh | 200Ah | 300Ah | 250-500 Watts |
The wattage and number of solar panels you would need depend not only on the size of the fridge but also on the amount of sunlight you receive.
For a thorough explanation, please refer to this guide: How many solar panels do I need to run a refrigerator?
Also, keep in mind that you would also need a solar charge controller. And in case your fridge runs on AC, an inverter would be required.
For more information, click here.