Calculate backup hours, usable energy, and savings. Adjust reserve, efficiency, battery age, and outage assumptions. Make confident power planning decisions for homes and businesses.
Enter battery, efficiency, reserve, and cost settings. The page uses a single-column flow, while the input grid responds as three, two, or one column.
| Load (W) | Voltage per Unit (V) | Capacity per Unit (Ah) | Series | Parallel | Usable Energy (kWh) | Runtime (Hours) |
|---|---|---|---|---|---|---|
| 300 | 12 | 150 | 2 | 2 | 4.08 | 13.59 |
| 500 | 12 | 200 | 2 | 2 | 5.44 | 10.88 |
| 1000 | 24 | 100 | 2 | 1 | 3.62 | 3.62 |
These examples assume practical efficiency, battery aging, and reserve settings. Real-world runtimes vary with temperature, discharge rate, cable losses, and inverter quality.
The calculator converts battery bank specifications into usable delivered energy, then divides that energy by the connected load.
Bank Voltage = Battery Voltage × Series Count
Bank Capacity (Ah) = Battery Capacity × Parallel Count
Nominal Energy (Wh) = Bank Voltage × Bank Capacity
Battery-Adjusted Energy = Nominal Energy × DoD × Battery Efficiency × Battery Health
Delivered Energy = Battery-Adjusted Energy × Inverter Efficiency for AC output
Usable Energy = Delivered Energy × (1 − Reserve Margin)
Backup Time (Hours) = Usable Energy ÷ Load Power
Recharge Cost = Usable Energy in kWh × Electricity Rate
Outage Value Covered = Backup Time × Outage Cost per Hour
Percent inputs are converted to decimals in the calculations. For example, 80% becomes 0.80.
Battery backup time is the estimated duration a battery bank can power a connected load before reaching the selected usable energy limit. It is usually expressed in hours and minutes and depends on load size, battery capacity, reserve margin, and efficiency losses.
Nominal energy is the installed theoretical battery energy. Usable energy is lower because practical systems lose energy through discharge limits, battery aging, inverter conversion losses, and the reserve margin kept for safer operation and longer battery life.
AC systems usually pass battery energy through an inverter. Inverters are not perfectly efficient, so some energy becomes heat during conversion. Because the load receives less delivered energy, the runtime becomes shorter than with an equivalent direct DC setup.
A reserve margin protects against measurement errors, aging, cold weather, and unexpected load spikes. Many users choose 5% to 20%. A higher reserve gives safer estimates but shortens the displayed runtime because more energy is intentionally left unused.
If all other settings stay the same, doubling usable energy will roughly double runtime. In real systems, cable loss, temperature, discharge rate, inverter behavior, and old batteries can reduce that perfect one-to-one scaling.
Use the expected financial impact of losing power for one hour. This could include spoiled inventory, lost work time, idle staff, reduced sales, interrupted internet service, or productivity losses in a home office or small business.
Amp-hour rating alone is not enough because voltage matters too. Energy depends on both voltage and amp-hours. A 24-volt bank with the same amp-hours stores about twice the energy of a 12-volt bank.
No. It is a planning tool for quick estimates and budgeting. Final system sizing should also consider surge loads, charger limits, discharge curves, ambient temperature, cable sizing, battery chemistry, inverter waveform, and applicable safety standards.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.