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There are many reasons why you would want to run a freezer off a battery. A camping freezer makes it easy to keep food fresh, while for homeowners it is a convenient backup in case of a power outage. But how many batteries will you need? And is it even possible?
A 12V 100ah battery can run a camping freezer fridge for about 50 hours, assuming the freezer draws 25-30 amps a day. A 15 cubic foot freezer requires at least a 12V 700ah battery to run for a single day.
How to Calculate Freezer Battery Requirements
To be clear, we are talking about freezers, not refrigerators. There is a separate guide for that here. There are basically two kinds of freezers, residential and portable, but calculations for both are the same.
Freezer watts per hour / voltage = amps per hour
Amps per hour x runtime = battery bank size
A standard 15 cubic foot freezer consumes 335 to 500 watts. Assume you have an Energy Star model that runs on 335 watts and you want enough battery power to run it for two days. Just in case of a power outage.
Most freezers can run on 240V, 120V and 12V. To power a 335 watt freezer for two days (48 hours) on 12V batteries:
335 / 12 = 27.9
27.9 x 48 = 1339
It takes 1339 amps to run a 15 cu. ft. freezer on 12 volts or at least 4 x 350ah batteries.
And those batteries will be fully drained with 3 days’ use. Deep cycle batteries are supposed to be recharged when capacity drops to 50%. If you adhere to this rule, the capacity must be doubled to 8 x 350ah batteries.
Most of the large freezers only draw 5 amps from a 120V power source. But with a 12V system the draw goes up to 40-50 amps, hence the need for more batteries.
Camping Freezer Battery Calculations
Camping freezers (also called camping fridge) are more economical. They are portable and designed to run on any 12V battery bank. They come in a variety of sizes, but most draw 1 amp an hour.
If you plan to go camping for three days and want to keep the portable freezer running, how many batteries are needed?
If the freezer draws 1 amp an hour, that would be 72 amps for 3 days. An 80ah battery can power the freezer for 3 days, but you should get a 150ah or 175ah battery so the discharge rate does not drop below 50%.
With a 175ah battery the freezer should last for a 3 day camping trip. If you have solar panels you can recharge the batteries and keep going for several more days.
If your freezer has a higher amp draw you can still use the same formula. Multiply the amps drawn per hour by the number of hours/days you want to run the freezer. Multiply the result by two and you have the ideal battery bank size.
1 amp per hour = 24 amps a day = 50ah battery bank
48 amps a day = 100ah battery bank
You only need to double the capacity if the battery has a 50% depth discharge rate. Batteries with higher discharge rates provide a longer runtime for freezers and other appliances.
How Long Will My Freezer Run on Batteries?
The answer depends on the runtime and battery depth discharge rate. The freezer size also plays a factor.
Freezer amps / battery size = runtime
A freezer that draws 5 amps an hour running on a 200ah 12V battery will run for 40 hours before the battery gets drained.
200 / 5 = 40
Again you should consider doubling the capacity to avoid completely draining the battery.
It should also be emphasized that these calculations are estimates only. Because of the way batteries run , the higher the amps drawn, the faster the discharge. The opposite happens if the amps drawn are low.
While a 200ah 12V battery might last for 40 hours, it is better to take a conservative approach and assume the runtime will be just under 40 hours.
The most practical approach is to note how many hours you want to run the freezer, and multiply the amps per hour by it. Double it as suggested earlier and you should be good to go.
So if you have a 2 amps an hour freezer and want to run it for a couple of days:
2 x 48 = 96
The freezer needs 96 amps to run for two days. 96 x 2 = 192. Rounded off you need a 200ah battery for a full two days’ use of the freezer. Again this assumes the battery has a 50% DOD but if it is better than that you can settle for a smaller battery bank.
Do I Need an Inverter to Power a Freezer?
It depends on the freezer. Most camping freezers run on 12V DC and can be hooked up directly to a battery bank and solar panels.
Residential freezers usually run on 120V, so you need an inverter to convert it to 12V if you want to run it on batteries. The inverter size will depend on the freezer.
Once the freezer is connected to the inverter, the system will draw power from the batteries and run. The runtime depends on how many amps the freezer draws and the battery size (refer to the calculations given earlier).
For portable freezers, you just need to have the right battery size and it is ready to go. As mentioned earlier the majority run on 12V, though some may work on 24V systems. A 24V system runs longer because it draws fewer amps, but not all freezers are designed to work with it.
Do I Need Solar Panels to Power a Freezer?
You can run a 12V freezer without solar panels, but it is better if you did. Solar panels allow you to recharge the batteries and operate the freezer for as long as there is sunlight.
Suppose you plan to go on a three day camping trip. You have a 12V freezer and a 150ah battery bank. At 1 amp an hour, the battery will last the three days without dropping below 50%.
But what if you decide to extend the trip? Maybe the scenery is really nice and you want to stay there for another day or two. Unfortunately the batteries are at the 50% discharge rate and there is no power source available. This is where solar panels come into play. By charging the batteries you can operate the freezer for as long as necessary.
A 100W solar panel can run a 60W freezer with plenty of power to spare. If you want to charge the batteries, make sure the solar panels are large enough to handle the capacity. A 100ah 12V battery holds 1200 watts, but you only need 600 watts to recharge it if you don’t let the power discharge below the halfway mark.
7 Tips to Run a Freezer on Solar Batteries
Plan ahead. Know how much food and beverages you will bring. This will tell you what freezer size and how many batteries are needed.
More power is better. If your calculations state the freezer needs 35ah, get a 40 or 50ah battery. It is better to have more power available than less.
Energy Star compliant. Use only energy efficient appliances for batteries and any solar power system.
Check the freezer specs. Freezers come in various styles, shapes and capacities. If there are several products that fit your needs, choose the most energy efficient one.
Power options. Some freezers may run on AC power only, particularly the large ones. But smaller models work fine with 12V DC. Always check the watts, amps drawn and supported voltage before you buy.
Charge the batteries first. Even if you have solar panels, give the batteries a full charge before you go on a camping trip.
Run the freezer from the batteries, not the solar panels. Solar panel power fluctuates depending on how much sunlight is present. Freezers need a consistent power source, which batteries can provide.
So to answer the question, yes you can run a freezer off batteries. You just need to know the freezer size and how long you intend to run it. Using the guidelines provided here you should have no problems whether the freezer is at home or camping.