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Easily calculate battery backup time for UPS, inverter, or solar systems with our free online Battery Backup Calculator. Fast, accurate, and user-friendly.
When the power goes out, having a reliable battery backup system is essential whether it’s for your home, office, or computer setup. But how do you know how long your battery backup will last? That’s where our Battery Backup Calculator comes in. This tool is designed to help you estimate the runtime of your UPS, inverter, or solar battery backup system based on simple inputs like battery capacity and power usage.
Whether you’re planning a home battery backup system or want to know how long your 150Ah inverter battery can support your appliances, our calculator gives you instant answers. It’s easy to use, beginner-friendly, and made for real-life situations.
Using the calculator is simple. You’ll need the following information:
Once you enter these values, the calculator will give you the estimated backup time in hours.
Here is the basic formula used to calculate battery backup time:
Backup Time (in hours) = (Battery Capacity (Ah) × Battery Voltage (V) × Efficiency) ÷ Load Power (W)
Where:
This means your 150Ah battery can support a 300-watt load for around 4.8 hours.
How long will a 500W UPS last on a 100Ah, 12V battery?
Backup Time = (100 × 12 × 0.8) ÷ 500 = 1.92 hours
How many hours will a 200Ah battery backup a 400W load?
Backup Time = (200 × 12 × 0.8) ÷ 400 = 4.8 hours
These examples are perfect for planning your UPS battery backup, inverter setup, or solar battery backup system.
For residential use, it's important to calculate the total wattage of essential appliances like lights, fans, router, refrigerator, and TV. Our home battery backup calculator helps you input each appliance and its wattage to give a detailed estimate of the total load and backup time.
This is ideal for:
Whether you are using a solar battery backup or a standard inverter, you can use the same formula. Just ensure you enter the correct voltage and battery size based on your setup.
Example:
If you have a 24V system with a 200Ah battery and a 600W load:
Backup Time = (200 × 24 × 0.8) ÷ 600 = 6.4 hours
This means you can run your 600W appliances for approximately 6.4 hours.
Lithium batteries usually offer better efficiency (up to 90–95%). To calculate accurately:
Backup Time = (Battery Capacity × Voltage × 0.9) ÷ Load Power
Lithium battery systems are ideal for critical backup power needs, like servers, medical devices, or sensitive electronics.
Choosing the right battery size and estimating your backup time doesn’t have to be confusing. With our Battery Backup Calculator, you can plan ahead and make smart decisions whether you're using a UPS, inverter, or solar battery system.
Use the formula:
Battery Backup Time = (Ah × V × Efficiency) ÷ Load in Watts
Add the total wattage of devices you want to power and use the formula to find how many amp-hours are required for your desired duration.
That depends on the battery size. A 100Ah, 12V battery can power it for approximately 1.9 hours.
A 200Ah, 12V battery can last around 4.8 hours with a 400W load.
Yes, the calculator supports solar battery backup calculations as well.
Yes. Just use 90% efficiency instead of 80% in the formula.