Inverter Battery Back up Time- How do we calculate?

Inverter Battery Back up Time- How do we calculate?

People who purchased an inverter battery for home, offices, or any other use will ask this question to their battery dealer “How long will the battery last”?. However, most battery store owners do not inform their clients of the actual numbers or the easy method for calculating the inverter battery back up time duration.

Inverter is one of the most needed appliances today because of this frequent power cuts.

Inverter systems are a frequent sight in our homes and offices, where they serve an important role in ensuring that sensitive loads and gadgets receive uninterrupted power. Inverters must be appropriately sized for household applications in order to satisfy the projected load demand. Do not worry readers, I will provide the easy formula right today to calculate your Inverter Battery Back up Time.

Before moving to the process to calculate the Inverter Battery backup time, we need to know the components of an Inverter Battery.

Basics of an Inverter Battery

An anode, a cathode, and an electrolyte are the three fundamental components of an inverter battery. If the electrolyte is insufficient, a separator is frequently put in place to keep the anode and cathode from contact. Batteries generally have some type of housing to contain these components.

How to Calculate Inverter Battery Back-up Time?

Inverter Battery Back up Time

The battery backup duration in an inverter is based on how much batteries are connected and their efficiency in Ampere/hours. Usually, you can expect your inverter battery to last anywhere from 6 to 10 hours when it is fully charged.

The battery backup time of an inverter is determined as follows:

Back up Time of Inverter Battery(hours) =  Voltage of the battery (V) x Batter Capacity(in Ampere/Hour) / Total loads taken in watts (W)

We can use symbols to simplify the formula instead of using lengthy words:


BT=  Time of Battery Backup taken in hours

Bc= Battery Capacity in Ampere hour

V= Voltage of battery taken in volts

TL= The load connected taken in watts (W)

Now According To Formula:

BT = BC x V / TL

Now let us figure it out with an example to understand better

If you have an inverter battery of 150Ah capacity with a voltage of 12 Volt. Let’s say you have 1 desktop, 1 ceiling fans, and two bulbs that are connected to the battery. How much is the backup time of your Inverter battery? Let’s do the math.

The total load can be assumed as

  • 2 bulbs = 30 x 2 = 60 Watts
  • 1 desktop computer= 170 Watts
  • 1 Ceiling Fan = 70 Watt

Here the total load is 60 + 170 + 70, which is equals to 300 Watts.

Now, as per the formula above, BC = 150, V = 12, TL =300

Battery Back up Time (hours) = 150 x 12 / 300 = 6 hours.

So, here in this case, your inverter battery is expected to lasts 6 hours of back up time.

You can use this calculator as well to determine the back up time.


  • These are estimated values of appliances’ wattage, checkout your appliance for exact wattage value.
  • Be sure to put all the values in SI units or metric systems to get an accurate answer.

Also this answers is somehow not accurate. Let me tell you the reasons why.

There will be some energy loss while transferring 12-volt battery power to 220 volts through an inverter, this number is merely an estimate.

Furthermore, because the ceiling fan includes a speed-adjustable dimmer switch, we are unable to determine the precise power usage. When the fan is running at a low speed, the power consumption is low.

Observation: (Energy usage of some old fans with big sized Regulator remains constant at all speed points)

Tips to get maximum output from your Inverter Battery.

To increase the output and stand by time of your inverter battery, make sure you follow these tips:

  • Turn off Unnecessary Appliances? Decrease the Load

    You may immediately increase the backup time by lowering the load. Because there are fewer appliances when there is less demand, your inverter will be capable of powering those lesser appliances for a longer period of time.
    If you are staying in one room, settle for less. You may only require one fan and one tube light at any given moment. As a result, ensure that some other rooms’ appliances are turned off so that the inverter has a light load.
  • Upgrade to a bigger Battery size.

    It is an understood thing; the Bigger the battery, the better the running time. Therefore, if you got tons of appliances in your home and you want to use all of them during the power cut then you must opt for a bigger size battery that can provide you with a better standby time and output.


Can I power a computer with an inverter?

Yes, you certainly can. Inverters can simply and safely power a computer without posing any danger. In reality, the output voltage of an inverter is frequently superior to that of the power system or dock power.
 This is why inverters, in partnership with a battery charger and a battery set, are frequently utilized as a backup system in areas where grid connections are problematic. An inverter may also be used to power laptops.

How long do you think my battery will last?

The life span of a battery is linked to how frequently it is discharged. If you live in an area with usual power cuts for hours then you should start worrying about replacing your battery soon. Because frequent discharges make the battery cells weak. But if you live in an area where there power cuts are rare, like around 3-4 hours per week then your battery can last 3-4 years.

Does the inverter calculate a backup time estimate?

Not all, but some premium quality inverters will tell you an estimated time on display. Although that is just an estimate, it is reliable with around 1-2 hours of error.

How can i know the Watt usages of my appliances ?

Generally the watt usages can be found on your appliances or else you can check it here on this website.


I am sure that this information will be very useful for you in keeping and maintaining your inverter and batteries. Some modern inverters come with a built in backup calculator and show you the remaining backup on the display while in some of the brands, you have to calculate it yourself using this simple yet helpful formula.

There are also some online battery backup calculators where you just have to input your information and it will do the rest of the calculation for you, you can use that too in order to get your backup time calculated.

For more specific information about your battery, please do check out the user manual that comes along with your battery for a better understanding of any complexities in your brand.

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