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There is no single answer to the question, how long can a 100ah battery run a fridge, because there are so many variables involved. The power required by the fridge, the voltage, the battery type and how batteries work all affect the runtime. This guide will walk you through the numbers.
A 100ah battery cannot run an average kitchen refrigerator because those require at least 300ah. However, a 60W portable fridge that draws 1 amp an hour can run for 20-25 hours on a 100ah battery that has a 50% discharge rate.
How Much Power Do Refrigerators Use?
A typical kitchen 120V refrigerator requires at least 1200W starting watts and 150W to 200W running watts. Factor in the on/off cycle and a fridge runs for about 8 hours a day, so it needs around 1000W or 1 kwh a day.
A portable fridge or camping fridge uses 60W to 185W a day. If you pack the food items already cold, power usage will drop off and save energy. The larger the fridge or solar freezer , the higher the wattage required.
These figures are for modern, Energy Star compliant units. Older refrigerators probably use at least 1500W during startup, and some even need 2000W or more. You should run those on solar batteries or any type of solar power.
If you are not sure how much power your refrigerator uses, it will be stated in the product manual or on the fridge itself. You can also find this info on the manufacturer website. Once you know the power requirements, you can determine if a 100ah battery like the Mighty Max ML 100 will be enough.
How Long Can My 100ah Battery Run a Fridge?
An easier way to gauge capacity is to use the 20 hour cycle. Most 100ah batteries can deliver 5 amps for 20 hours. So a 100ah battery can run a fridge for about 10 hours if it draws 5 amps an hour. After 10 hours the fridge will have drawn around 50 amps. Battery capacity will be at 50%, just in time for a recharge.
If you want to do more calculations, follow the guide below. Before we can run an estimate though, you have to know a few things:
- Refrigerator power consumption is measured in watts
- Battery capacity is measured in amps
- Amps x volts = watts
- Watts / volts = amps
- 1 amp is equal to 120W at 120V
You must also have the following information:
- The power required by the fridge, starting and running watts
- The battery voltage
- The battery type
- How many amps the fridge will draw
- How battery discharges work
A 120V refrigerator consumes 5 to 7 amps, but you must provide it with 15 to 20 amps during the startup. A 100ah 12V battery is equal to 1200W. This is the starting wattage required by most refrigerators, so why isn’t it enough?
In real life cases the battery won’t work for several reasons, because you can never use the full capacity. A 100ah battery can power a 60W fridge for a day if it draws 1 amp an hour. The higher the amp draw, the shorter the battery life.
Energy efficient kitchen refrigerators require 1200W minimum during startup, which is equal to the full capacity of a 100ah battery. So the starting wattage needed by the fridge will empty the battery already. This applies not just to refrigerators but to AC units and other appliances.
Why You Can Never Use Batteries at Full Capacity
A 100ah battery may have 100 amp hours, but you can only use 50ah if it is lead acid because it has to be recharged when the charge drops at 50%. Even a a 100% charged battery will not deliver full power when the capacity drops to 30% or lower.
As mentioned, battery amp hour capacity is measured in 20 hour cycles. A 100ah battery can supply 5 amps an hour for 20 hours. But use the battery more than 20 hours and it will no longer work at full power. The more a battery is discharged, the more power is lost. Heat, impedance and other factors affect the capacity too.
As explained here lead acid batteries – FLA, AGM and gel – only have half the stated capacity available for usage. If you need 100ah to run your camping fridge for a day, get a 200ah battery.
With lithium batteries like the FLYPOWER 12V you can wait until 75% to 85% or more. But most solar power users will tell you that it’s not a good idea to completely discharge it either. While lithium batteries are superior to lead acid, the life cycle will be shortened with frequent 0%-100% charging.
Both lead acid and lithium batteries charge the same way. A 100ah battery cannot run a 2 amp fridge for 50 hours, or a 1 amp fridge for 100 hours. With a 50% depth of discharge, you only get 50ah to work with.
5 Amps For 20 Hours Battery Capacity
Rather than compute 100ah literally, it is better to use the 5ah per 20 hour guideline given above. You will get a more accurate estimate of how long the battery will last.
Keep in mind though that these figures are not 100% accurate. 5 amps per 20 hours is fairly accurate as long as the capacity is 50% or higher. If it drops below 50%, the battery may no longer run at maximum power.
Drawing more amps will also affect the runtime. 5 amps for 20 hours does not necessarily mean 10 amps for 10 hours. The more amps drawn, the faster your 100ah will discharge, so it could be 9 or 10 hours.
When you use a solar battery to turn on a light bulb it will not use a lot of power. But if you power a refrigerator, the battery will generate heat, taxing its internal components. The hotter it gets, the harder it becomes for the battery to provide the energy required. That is why drawing more amps will not generate more power, only reduce the battery efficiency.
Tips For Running a Fridge with a 100ah Battery
While you cannot run a 20 cubic foot refrigerator, you should have no problems running a portable fridge. To make the battery last longer, here are some tips.
- Choose the right fridge. Know what type of fridge you want to use, how many watts it consumes, the amps per hour it draws and how long you intend to run it on the battery. A lot of the problems with power consumption stems from lack of planning. If you plan ahead you will be prepared for any power emergency.
- Choose the right battery. If you have a 100ah battery, decide if it will be 12V, 24V etc. Decide if you want to go with lead acid or lithium ion. Lithium ion costs more but lead acid is more widely available. If you are only going to use the fridge for a few hours a couple of days, lead acid will be fine.
- Chill the food before storing it in the fridge. This will reduce the amount of power needed. You can do the same thing with beer cans. If you only bring beverages during your trips, you can opt for a freezer instead of a fridge.
- Choose an energy efficient fridge. The difference between an Energy Star compliant and one that isn’t is significant. You will get several more hours of use with an energy efficient fridge.
Here is an example. if you are boondocking and want to bring a camping fridge, check how many amps it will use. If you have an Engel fridge that draws 5 amps and you have a 100ah lead acid battery, you can run the fridge for 10 hours. But if you have a 2 x 100ah batteries you can run the fridge for 20 hours. If your battery is lithium and the fridge draws 2.5 amps, runtime will be even longer.
You should always overestimate power requirements. With inverters, solar panels and chargers, we recommend 10%-20% or more reserve. The same rule applies to batteries. You should get a couple of 100ah batteries if you plan to connect more than the fridge to the system.
One thing about solar batteries is you don’t have to worry about the weather. Unlike solar panels, you can use the battery day night, sunny or rainy weather. Just make certain the battery is fully charged for the fridge. If you expect the fridge will require more than 100ah, either get another 100ah or connect the battery to a solar panel.
If you are going to use a solar panel with the battery, you have to account for sunlight hours. This is crucial especially if your fridge contains food that could get spoiled. In other words, you should plan for the weather, regardless of what it will be.
The refrigerator is one of the most power hungry appliances today, so it’s no wonder a lot of math is involved. The bottom line though is a 100ah battery can run a portable fridge, though the duration depends on its usage. If you plan to run a refrigerator on batteries, make sure there is sufficient power available.