Size the battery for your load.
Work backwards from load and runtime to get the nominal kWh, usable energy, pack count and an energy-level series-parallel estimate.
How much battery do you need?
Start with the load and the hours you need to cover. The calculator applies DoD and system efficiency before rounding up to real packs.
The battery kWh sizing formula
The sizing chain is simple: calculate the energy the load needs, then increase it for the portion of the battery that is usable and the energy lost during conversion.
This is a first-pass capacity estimate. Real projects also check peak load, temperature, aging reserve, battery current, inverter limits and the required backup operating mode.
What the result means
- Usable kWh
- The energy that should reach the load during the requested runtime. This is the operational requirement.
- Nominal kWh
- The nameplate capacity required before the DoD and system-efficiency allowances are applied.
- Pack count
- The minimum number of single batteries needed to reach the nominal energy target. The result always rounds up.
- Series × parallel
- An energy-level string estimate. Series packs meet the target DC voltage; parallel strings provide the required capacity.
FAQ
How do I calculate battery kWh from load and runtime?
Multiply the average load in kW by the required runtime in hours to get required usable energy. Then divide by DoD and system efficiency to estimate the nominal battery energy.
What is the difference between usable and nominal kWh?
Usable kWh is the energy you intend to deliver to the load. Nominal kWh is the nameplate capacity required after accounting for the battery operating window and conversion losses.
How many batteries do I need?
Divide the minimum nominal kWh by the capacity of one battery and round up. This calculator also rounds the energy count into an estimated series and parallel layout.
Why does the calculator need DoD and efficiency?
A battery is not normally discharged to zero, and energy is lost in the inverter and other conversion steps. Including both factors prevents a first-pass design from being undersized.
Is the series and parallel layout final?
No. It is an energy-level estimate based on the target and single-pack nominal voltages. A final design must confirm inverter voltage windows, BMS limits, current, protection and local installation requirements.
Share the load profile — we will check the design
Hua Power can validate the duty cycle, voltage platform, usable reserve and product configuration behind the first-pass number.