How to Calculate Inverter Battery Capacity:
Follow the steps and examples below.
1. Calculate the total load (watts):
The larger your battery capacity, the more load it can carry in a given time frame.
For example, let's say you want to power five 30-watt LED lights and two 80-watt laptops. In this case, the total load will be:
5 x 30 + 2 x 80 = 310 watts
Therefore, the load on the inverter will be 310 watts per hour.
The power rating of each appliance is usually mentioned on the appliance's packaging. Use our simple load calculator to calculate wattage requirements per hour.
Note: Calculate the load demand for only those devices that you plan to use during a power outage by connecting to the inverter.
2. Estimated usage time (in hours):
How long you want the battery to keep running your appliance when the power is off. You can estimate this by calculating the average duration of outages in your area.
For example, typically, if your area has a power outage of up to 3 hours, that means you typically need 3 hours of backup power.
3. Check the battery input voltage:
In the market, almost all inverter batteries have an input voltage of 12V. Other 24v/48v/60v battery systems, etc., can be obtained by connecting 12v battery units in series. You can learn about the connection methods of different battery systems in your product or user manual
4. Find the battery efficiency percentage:
Generally, it is inevitable that the inverter will lose some energy when discharging. This discharge efficiency varies from inverter to inverter, all major brands of inverters provide 80% i.e 0.8 , and high quality inverters can provide more than 90%
5. Calculate the battery capacity (AH):
Battery Capacity = (Total Load (W) X Usage Time) / (Input Voltage X Efficiency %)
To understand the above formula, assume the following numbers.
Total load: 310 watts
Usage time: 3 hours
Input voltage: 12V
(310 X 3)/(12 X 0.8) = 96.875
So a battery with a capacity of 96.875Ah should work well in this case. There may not be batteries of the same capacity on the market, so you can buy battery above 100 ah, such as 100Ah or 150 Ah battery.
The above calculations assume voltage – 12v; battery efficiency – 80%.
There may not be exact capacity requirements on the market, so choose a battery with a higher capacity.
Common capacity batteries are – 80, 100, 120, 135, 150, 180, 200, 220 AH. For loads above 600 watts per hour, planned for 3 hours running, it is recommended to purchase >1 220 AH batteries to meet the requirements.
Also, for some inductive loads, such as refrigerator , freezer , microwave, water pump, air conditioners and other appliances with compressors or motors, their instantaneous power in startup phase is 6-7 times ,or even 10 times bigger as it's working power, In this case, it is necessary to increase the battery capacity according to the load situation, otherwise the battery capacity may not be enough to support the inverter to supply power to the load.