Renewable Energy calculator
Battery Capacity Calculator
A 0.5 kW load for 4 hours delivers 2.0 kWh; with 80% DoD, 90% efficiency, 100% temperature factor, and 15% margin, the bank calculates at about 3.19 kWh nominal or 266 Ah at 12V. A 48V solar storage case at 10 kWh/day for 2 days can also translate the result into a 4-series by 8-parallel, 32-module LiFePO4 block when 12.8V, 100Ah modules are entered. This battery capacity calculator converts load energy into required nominal battery kWh, amp-hours, and optional battery unit count after depth of discharge, discharge-path efficiency, temperature capacity factor, and design margin. It is intended for honest battery-bank sizing, not for replacing a UPS manufacturer runtime chart, a battery manufacturer discharge table, or a full ESS equipment submittal review.
Updated July 16, 2026
A 0.5 kW load for 4 hours is 2.0 kWh delivered. With 80% DoD, 90% efficiency, and 15% design margin, the bank screens at about 3.19 kWh nominal or about 266 Ah at 12V. A 48V solar storage bank at 10 kWh/day for 2 days screens at about 37.58 kWh nominal and about 783 Ah, or about 32 LiFePO4 modules when 12.8V 100Ah units are entered.
Nominal battery kWh = delivered load kWh ÷ (DoD × efficiency × temperature factor), then add design margin. Battery block screen = series count from bank voltage and parallel strings from required Ah.
Choose daily energy, load-and-runtime, or peak-shaving mode below to screen nominal battery kWh, amp-hours, and optional battery unit count
Example Calculations
How to Use
What this battery capacity calculator actually sizes
This page sizes nominal battery-bank capacity. It does not try to guess warranty life, choose a BMS, select a PCS or inverter, or replace manufacturer discharge tables. Instead, it answers a narrower question: how much nominal battery energy is needed to deliver the required load energy at the selected depth of discharge and planning factors? When a battery unit voltage and amp-hour rating are entered, it also screens series count, parallel strings, total battery units, configured kWh, and capacity margin.
For solar-plus-storage, pair this page with the inverter sizing calculator, the battery capacity runtime chart, and the solar planning hub so the storage screen stays tied to the wider solar workflow.
The three sizing workflows on this page
| Workflow | When to use it | Load basis |
|---|---|---|
| Daily energy + autonomy | Solar storage, off-grid backup, and longer-duration planning | Daily kWh multiplied by required autonomy days |
| Load + runtime | Battery-bank sizing from a known kW load and target hours of support | Load kW multiplied by runtime hours |
| Peak-shaving discharge window | Energy screening for a planned shave block | Shaved kW multiplied by the planned shaving window |
The core sizing equation
Required nominal battery kWh = Delivered load kWh ÷ (DoD x discharge efficiency x temperature factor), then adjusted upward by the selected design margin.
Once nominal battery kWh is known, the page converts that energy into amp-hours from the selected DC bus voltage:
Required battery Ah = Required nominal battery kWh x 1000 ÷ DC bus voltage
If battery-unit data is entered, the configuration screen uses:
Series units = ceil(bank voltage ÷ unit voltage)
Parallel strings = ceil(required Ah ÷ unit Ah)
Total units = series units x parallel strings
Configured kWh = unit voltage x unit Ah x total units ÷ 1000
Why depth of discharge matters
Depth of discharge changes how much of the battery bank you plan to use. A 20 kWh nominal bank at 80% usable depth of discharge is not a 20 kWh usable bank for planning purposes; it is a 16 kWh usable-energy screen before other planning factors such as efficiency or temperature are applied.
| Battery chemistry | Common planning range | What this means in practice |
|---|---|---|
| Flooded lead-acid | Often screened near 50% DoD | Requires a larger nominal bank for the same delivered load energy |
| AGM / Gel | Often screened conservatively around 50% DoD | Still benefits from conservative runtime planning |
| Lithium-ion | Often screened around 80-85% DoD | Usually allows a smaller nominal bank than lead-acid for the same delivered energy |
| LiFePO4 | Often screened around 80-90% DoD | Common for storage banks that need a deeper usable window with good cycle life |
Why the temperature factor and design margin are separate
The temperature factor adjusts for capacity reduction during the expected discharge condition. The design margin is separate headroom for aging, uncertainty, and project-level conservatism. Keeping those inputs separate makes the math easier to review.
Battery block and module count screen
The optional battery-unit fields turn the required bank size into a first-pass configuration. For example, a 48V storage bank that needs about 37.58 kWh nominal and 783 Ah can be screened with 12.8V, 100Ah LiFePO4 modules. The calculator rounds up to 4 units in series and 8 parallel strings, or 32 total modules. That configured block provides about 40.96 kWh nominal, with about 9.0% capacity margin above the required bank screen.
Use the parallel-string planning limit as a review flag, not as an approval. If the screened bank needs more parallel strings than the entered limit, review larger battery modules, a different DC bus voltage, a listed ESS architecture, manufacturer instructions, and installer/AHJ expectations.
How this page relates to UPS runtime and inverter sizing
If you need a UPS runtime screen, use the UPS backup time calculator, because UPS runtime is strongly shaped by the exact UPS model, battery string arrangement, and high-discharge behavior. If you are building a solar-plus-storage system, pair this page with the inverter sizing calculator and the solar calculator.
What this page does not claim
- It does not replace a manufacturer discharge curve or runtime chart.
- It does not approve the final battery series/parallel configuration or listed ESS architecture.
- It does not size battery protection, conductors, PCS equipment, or charging sources.
- It does not model tariff economics or dispatch optimization for peak shaving.
- It does not certify code compliance by itself.
Worked runtime example
Suppose a backup load is 0.5 kW for 4 hours. The delivered load energy is 2.0 kWh. With 80% depth of discharge, 90% discharge efficiency, 100% temperature factor, and a 15% design margin, the nominal bank screen becomes:
Nominal battery kWh = 2.0 ÷ (0.80 x 0.90 x 1.00) x 1.15 = about 3.19 kWh
At 12V DC, that lands at about 266 Ah of nominal battery capacity.
That result is useful as a planning screen, but the final battery-bank decision should still be checked against manufacturer discharge data, allowed current, environmental conditions, and the rest of the DC and AC system design.
Common Applications
More applications. Open to review 4 additional use cases.
Frequently Asked Questions
How do I calculate battery capacity from load and runtime?
First convert the load into delivered energy: load kW x runtime hours. Then divide by the allowed depth of discharge, discharge-path efficiency, and temperature factor to find required nominal battery kWh, and finally add design margin. Convert that nominal kWh into amp-hours with nominal battery kWh x 1000 ÷ DC bus voltage.
Why is the required battery bank larger than the load energy alone?
Because the battery bank cannot usually deliver 100% of its nameplate energy to the load. Depth of discharge limits usable capacity, discharge-path efficiency reduces delivered energy, temperature can reduce available capacity, and many designs include extra headroom for aging and uncertainty.
Can I use this page as a lithium battery size calculator?
Yes, as a planning screen. The page supports lithium-ion and LiFePO4 chemistry choices so you can apply a more realistic planning depth of discharge. Final limits still depend on the specific battery product and its BMS, so manufacturer data always wins over a generic calculator.
How do I estimate the number of batteries or modules?
Enter the battery unit voltage and amp-hour rating. The calculator rounds up the series count from bank voltage divided by unit voltage, then rounds up parallel strings from required Ah divided by unit Ah. The result is a planning block count, not a final listed system design.
Does this page replace a UPS runtime chart?
No. UPS runtime depends heavily on the exact UPS model, the battery pack arrangement, and the high-discharge behavior of the batteries. This page sizes battery-bank energy. For UPS runtime screening, use the dedicated UPS backup time page and then confirm the result against the manufacturer runtime chart.
Can I use this page for peak shaving?
Yes, but only as an energy screen. Enter the planned shave power and the discharge window to estimate required battery-bank energy, then verify the final design with the PCS power rating, dispatch logic, tariff structure, charge-recovery time, and manufacturer limits.
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