How to Size Battery Backup for Refrigerator: A Comprehensive Guide

Ensuring your refrigerator continues to operate during power outages is crucial for preserving food and preventing spoilage. A battery backup system can offer the reliability you need. However, determining the appropriate battery size requires careful consideration of several factors.

In this guide, we will walk you through the process of sizing a battery backup for your refrigerator, providing you with the knowledge to make an informed decision.

Assessing Your Refrigerator’s Power Requirements

Determine Power Consumption 

The power consumption of an appliance is measured in kWh, which means kilowatt hours. Now, one kWh is equal to running a 1 kW appliance for 1 hour, or a 2 kW appliance for 30 minutes.

However, the actual power of appliances could be different from their rated power. Air conditioners and refrigerators are two appliances whose actual power is different from their rated power. During the start of these appliances, they consume peak power, but once the temperature reaches to set value, their power consumption reduces.

The rated power of a home refrigerator is typically between 900 to 2,400 watts. However, their actual power consumption is 1/3 of rated power, that is, 300 to 800 watts per hour. 

Hence, to calculate the battery size for a refrigerator, you must consider its running power instead of its rated power.

To simplify the same, please check the Energy Guide Label of the refrigerator. Refer to two examples of Energy Guide labels for a 3.2 cubic feet refrigerator and a 23 cubic feet Refrigerator. 

Calculate Daily Energy Usage 

Next, calculate the hourly kWh consumption of your refrigerator. To calculate the same, first calculate daily power consumption by dividing the estimated yearly power consumption of your refrigerator by 365. Then, divide the per-day power consumption by 24 to get the hourly power consumption. 

So, for a 23 cubic feet refrigerator hourly power consumption will be equal to (630/365/24=) 0.072 kWh (approx.), and for a 3.5 cubic feet refrigerator,r the same will be equal to (206/365/24=) 0.024 kWh (approx.).

Calculate hourly Energy Usage 

Now, convert the power consumption from kilowatt hours (kWh) to watt hours (Wh) by multiplying kWh by 1000.

for 23 cubic feet refrigerator = 0.072 x 1000 = 72 Wh

for 3.2 cubic feet refrigerator = 0.024 x 1000 = 24 Wh

Sizing the battery

To calculate the size of the battery for the backup of a refrigerator, some factors need to be considered.

1. Backup time: The Longer the backup time, the higher the battery size.

2. Aging factor: As time passes, the backup capacity of the battery reduces; hence, a 1.1 to 1.25 aging factor needs to be considered. For best results, use 1.25 as the aging factor.

3. Depth of discharge: Discharging batteries below their Depth of discharge frequently reduces the life of the battery.  Moreover, the depth of discharge for a battery is dependent on the type of battery.

a. Lead Acid Battery: 50%

b. Deep-cycle Lead Acid batteries: 80%

c. Lithium ION: 80-90%

Furthermore, discharging batteries below their depth of discharge occasionally won’t make any difference in their life span. So, if the frequency of power outage is lower than discharging lead acid batteries up to 80% won't make any difference in the life span of batteries. 

4. Temperature correction factor: The battery gives higher backup at room temperature and higher temperatures, and the battery gives lower backup at lower temperatures. Hence, a temperature factor is required to compensate for the same. The temperature correction factor also depends on the type of battery.

   

Some thumb rules for the same are mentioned below.

Temp	Lead Acid	Lithium
above 50°C	0.8	0.96
40-50°C	0.9	0.98
25-30°C	1	1
10-20°C	1.2	1.02
0-10°C	1.3	1.04
Below 0°C	1.5	1.08

5. Inverter efficiency: No system in this world is 100% efficient, so is the battery system. Most have an efficiency rating between 85% and 95%. To ensure your battery backup can adequately support your refrigerator, account for these efficiency losses.

   
   

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Battery sizing for a refrigerator 

Battery size for a refrigerator can be determined by using the following formula.

Battery size =

Refrigerator hourly power usage x Backup time x Aging factor x Temp correction factor x (1/ Depth of Discharge factor) x (1/system efficiency) x (1/Battery Voltage)

Battery capacity is measured in ampere-hours (Ah). To determine the required battery capacity, divide the refrigerator’s energy usage by the battery voltage. Most household batteries are 12V. Moreover, you will also find 24V batteries. Aslo, read 12V vs 24V battery

Example:

Refrigerator size	23 cubic feet	3.2 cubic feet
Yearly power consumption	630 kWh	206 kWh
Daily power consumption	630/365 = 1.73 kWh	206/365 = 0.56 kWh
Hourly power consumption	1.73/24 = 0.072 kWh	0.56/24 0.023 kWh
Hourly power consumption in Wh	0.072 x 1000 =72 Wh	0.023 x 1000 23 Wh
Backup time	10 Hours	10 Hours
Aging factor	1.25	1.25
Temp correction factor for 30 °C	1	1
Depth of discharge	50% (Lead Acid) 80% (lithium & deep cycle)	50% (lead Acid) 80% (lithium & deep cycle)
System efficiency	90%	90%
Battery size (lead acid)	72 x 10 x 1.25 x 1 x (1/0.5) x (1/0.9) x (1/12) = 166 Ah	23 x 10 x 1.25 x 1 x (1/0.5) x (1/0.9) x (1/12) = 53 Ah
Battery size (Lithium & deep-cycle battery)	72 x 10 x 1.25 x 1 x (1/0.8) x (1/0.9) x (1/12) = 104 Ah	23 x 10 x 1.25 x 1 x (1/0.8) x (1/0.9) x (1/12) = 33 Ah

 Since, above calculated battery sizes are not standard battery sizes, please refer to the table below for the standard battery sizes needed to run 23 cubic feet & 3.2 cubic feet refrigerator for 10 hours.

Lead-acid battery

Refrigerator size	23 cubic feet	3.2 cubic feet
Backup hour	10	10
Battery size	180Ah or 200Ah	60 Ah

Do you know? Why are batteries rated in Ah? Click here to read our complete guide on the same.

Lithium-ion battery

Refrigerator size	23 cubic feet	3.2 cubic feet
Backup hour	10	10
Battery size	100 Ah	40 Ah

Selecting the Right Battery Type

Types of Batteries

There are several types of batteries available for backup systems, including lead-acid, lithium-ion, and AGM (Absorbent Glass Mat) batteries. Each type has its advantages and disadvantages in terms of cost, lifespan, and efficiency. 

• Lead-acid batteries are cost-effective but heavier and require maintenance.

• Lithium-ion batteries are lightweight, have a longer lifespan, and require minimal maintenance, though they are more expensive.

• Deep-cycle lead-acid batteries offer a balance between cost and performance and are maintenance-free.

  
  

Installation and Maintenance Tips

Proper Installation Practices

Ensure your battery backup system is installed correctly. Follow manufacturer guidelines and consider consulting a professional if necessary. Proper installation can prevent damage and ensure optimal performance.

Regular Maintenance

Regularly inspect your battery backup system for signs of wear or damage. Clean battery terminals and check connections to maintain efficiency. For lead-acid batteries, monitor electrolyte levels and refill as needed.

Conclusion: Making an Informed Decision

Sizing a battery backup for your refrigerator involves understanding power requirements, selecting the right battery type, accounting for efficiency losses, and planning for extended outages. By following these steps, you can ensure your refrigerator remains operational during power failures, protecting your food and peace of mind.