HOW TO CALCULATE INVERTER BATTERY CAPACITY: THE FORMULA
Have some difficulty in calculating the inverter battery capacity from the above table? Follow the steps and examples below.

1. CALCULATE THE TOTAL LOAD (IN WATTS):
This is the total load your inverter battery will be able to carry. The more capacity your battery has, the more load it will be able to carry for long hours.

So, it comes down to the number of appliances you want to power with your inverter.

As an example, let’s assume you want to power, 4 lights of 40 watts and 3 fans of 75 watts each. The total load, in this case, will be:

4 x 40 + 3 x 75 = 385 Watts

Hence, the load on the inverter will be 385 watts per hour.

The watt that each appliance uses is usually mentioned in the package of the appliance. Use our simple load calculator to calculate the Watt requirement per hour.

Note: Calculate the load requirement of only those appliances which you have connected to the inverter or planning to use during power cuts by connecting to an inverter.

2. ESTIMATE THE USAGE TIME (IN HOURS):
This simply means, how long do you want the battery to last when there is a power shutdown. You can estimate this by calculating the average time of power cut your area gets.

For example, usually, if power cuts in your area are 3 hours long, that means that you would usually need a power backup of 3 hours.

One should go for a minimum of 3 hours back up time considering Indian climatic conditions and resource availability.

3. CHECK THE BATTERY INPUT VOLTAGE :
This simply means the voltage of the battery. In India, almost all the inverter batteries have 12V of the input voltage. You can check this in your product or user manual.

4. FIND OUT THE BATTERY EFFICIENCY %:
While discharging current by inverter there could be some loss of energy, which is unavoidable. This efficiency of discharge varies from the inverter to the inverter, which you can find in the product catalog or product manual. In general, all the major brand’s inverter delivers 80% i.e 0.8 efficiencies.

5. CALCUATE THE BATTERY CAPACITY (AH):
FORMULA:

Battery Capacity = ( Total Load In Watts X Usage time ) / (Input voltage X efficiency %)

To understand the above formula, Assume the following numbers.

Total Load: 385 Watts
Usage Time: 3 Hours
Input Voltage: 12V
Efficiency : 0.8
(385 X 3)/(12 X 0.8) = 120.3125

Therefore, in this case, a battery with 120.3125 Ah of capacity should serve well. Same capacity batteries may not be available in the market, so you can go for those above 120 ah e.g 150 Ah battery.

Also Read: 10 BEST INVERTER BATTERY FOR HOME IN INDIA 2021

BATTERY CAPACITY TABLE – BACKUP TIME VS LOAD – FOR QUICK REFERENCE:
We have created a Backup time vs load comparison table for your ready reference to take an appropriate decision.

BACKUP TIME VS LOAD 100 WATT 200 WATT 300 WATT 400 WATT 500 WATT 600 WATT 700 WATT
3 HOURS 31.25 AH 62.5 AH 93.75 AH 125 AH 156.25 AH 187.5 AH 218.75 AH
4 HOURS 41.7 AH 83.33 AH 125 AH 166.67 AH 208.33 AH 250 AH 291.67 AH
5 HOURS 52.08 AH 104 AH 156 AH 208.33 AH 260.4 AH 312.5 AH 364.6 AH
6 HOURS 62.5 AH 125 AH 187.5 AH 250 AH 312.5 AH 375 AH 437.5 AH
7 HOURS 73 AH 145.83 AH 218.75 AH 291.67 AH 364.6 AH 437.5 AH 510.4 AH
8 HOURS 83.3 AH 166.7 AH 250 AH 333.33 AH 416.67 AH 500 AH 583.33 AH
10 HOURS 104.17 AH 208.33 AH 312.5 AH 416.67 520.83 AH 625 AH 729 AH
Note:

Above Calculations are made assuming, Voltage – 12v; Battery Efficiency – 80%.
Exact capacity requirement may not available in the market, so go for near higher capacity battery. Common capacity batteries are – 80, 100, 120, 135, 150, 180, 200, 220 AH.
For loads above 700 Watt per hour, it is recommended to buy >1 battery to fulfill the requirement.
Also Read: 10 BEST INVERTER BATTERY FOR HOME IN INDIA 2021

FREQUENTLY ASKED QUESTIONS:
1. Is a higher AH battery is better?
The higher the AH, the higher its capacity to store the charge and power appliances for a longer time. Higher Ah provides higher running or backup time.

However, a higher AH battery comes at an extra expense, weight, and volume; so calculate your capacity requirement and take a prudent decision. We recommend you going for min 150 AH though your capacity requirement is less than 150 AH.

2. How Many AH do I need for home?
It depends on your load requirements, frequency, length of power cuts in your area. In general 150 AH capacity is good for home. Calculate the capacity requirement using the table or calculator above to decide the best-suitable capacity for your home requirement.

3. How many watts is a 150 ah battery?
Assuming battery input voltage 12v, a fully charged 150 AH can discharge 150(AH)*12(V) = 1800 Watt-hour ideally.

But there could’ve some energy loss while discharge, so at 80% battery efficiency – it can deliver 1800 WH*80% = 1440 WH i.e It can provide 1440 watt current for 1 hour or 720-watt current for 2 hours.

1440 WH is equal to 1.44 Unit current.