How to Calculate Inverter Battery Backup Time?

Whenever you plan to buy an inverter battery, there is a desire to know some important information in your mind. Like how much will be the backup of the inverter battery, how many hours of backup will be available for how many ah batteries, etc. In this informative information, here you will know the backup time calculation formula. 


Backup Time Calculation Formula:

Backup Time = Battery Capacity (in Ah) * Battery Voltage (in V) * Battery Efficiency (in %) / Connected Load (in W/h)

For example:

Case 1: Lead Acid Battery

If you have any capacity of lead acid battery (80Ah to 200Ah), then you can calculate battery backup time as per below example. I have taken here the most popular inverter battery 150Ah battery. When we calculate battery backup time of any type of battery, we ideally use 400-watt home load, so the connected load is 400 watts per hour. Let’s calculate backup time now:

Backup Time = 150Ah * 12V * 0.75 / 400 W

                        = 1350 W / 400 W

                        = 3.3 hrs.

Note: An efficiency of lead acid battery is approx. 70% to 75%

That means, if we run 400-watt home loads on 150Ah inverter battery, then it gives approx. 3 hr. 30 minutes backup time. Depending upon backup time, you can choose battery capacity.

Case 2: Lithium Battery

If you choose a lithium battery for home inverter such as 100Ah, 12.8V, then you can calculate backup time as per above formula. All parameters will be same, let’s know backup time of lithium battery:

Backup Time = 100Ah * 12.8V * 0.98 / 400 W

                        = 1254 W / 400 W

                        = 3.13 hrs.

Note: An efficiency of lithium battery is approx. 95% to 98%.

That means, if we run 400-watt home loads on 100Ah lithium inverter battery, then it gives approx. 3 hr. 15 minutes backup time. Like this example, you can calculate backup time of CAML 100, 5kWh lithium inverter battery.

Source: Himanshu Chaprana, Student of B. Tech (Electrical & Electronics Engineering) - Manav Rachna International University, Faridabad, Haryana

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Hello Eng. How can I calculate the backup time for 2 batteries connected in series, 200ah/12v lead acid, supplying a load of 450w. Thx



Hello sir , how do I calculate battery backup time for two batteries each 200ah, 12v lead acid connected in series with a load of 450w?

Padmaraja Jinnappa Dulappanavara

Padmaraja Jinnappa Dulappanavara

Looking for laptop UPS backup

Syed afaq

Syed afaq

Hi sir . Plz tell me about battery .
My load DC 5 amp. And run it about 7hors .
Battery capacity??

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