What is Battery Backup Calculator?
Battery Backup Calculator helps you estimate battery runtime from usable stored energy and connected load.
The main result is estimated backup time, with a breakdown of usable delivered energy. The formula, example and assumptions below explain how to interpret it.
How to use Battery Backup Calculator
Use the example to get familiar with the form, then enter your own figures. Any rates in the example are illustrative. Check the field labels and units before calculating.
- Gather battery bank voltage (V), battery bank capacity (Ah), usable depth of discharge (%), inverter / UPS efficiency (%) and connected load (W). Use values from the same situation or reporting period.
- Replace the example battery bank voltage with your own value, then complete the other fields. Check the displayed units.
- Select Calculate and read estimated backup time with its result breakdown. Change one input and calculate again to compare a second scenario. Reset restores the original example.
- Enter battery bank voltage in V, at least 0.000001. Decimals are accepted.
- Enter battery bank capacity in Ah, at least 0. Decimals are accepted.
- Enter usable depth of discharge in %, at least 0 and at most 100. Decimals are accepted.
- Enter inverter / UPS efficiency in %, at least 0 and at most 100. Decimals are accepted.
- Enter connected load in W, at least 0.000001. Decimals are accepted.
Battery Backup Calculator: a worked example
With the inputs below, the result is 4.896 hours (estimated backup time). Follow the example, then replace these illustrative values with your own.
| Input or output | Example value |
|---|---|
| Battery bank voltage (V) | 24 V |
| Battery bank capacity (Ah) | 150 Ah |
| Usable depth of discharge (%) | 80 % |
| Inverter / UPS efficiency (%) | 85 % |
| Connected load (W) | 500 W |
| Estimated backup time | 4.896 hours |
| Usable delivered energy | 2,448 Wh |
Understanding the Battery Backup result
Read estimated backup time alongside usable delivered energy. These describe different parts of the same calculation.
Displayed results use a readable number of decimal places. When checking a result by hand, keep extra precision until the last step. To compare scenarios, change one input at a time and keep the others fixed.
- Example Usable delivered energy: 2,448 Wh
Battery Backup Calculator: assumptions and common mistakes
A useful estimate starts with the right inputs. Check the following assumptions and limits before applying the result to your situation.
- Nominal-energy estimate. Battery age, discharge-rate effects, temperature and surge loads can reduce runtime.
- DC, single-phase and three-phase calculations use different relationships. Equipment selection also depends on installation conditions and applicable standards.
For wider guidance, visit Bureau of Indian Standards. The formula and scope of this specific tool are stated on this page.
