Metric Republic / Energy & building physics / Battery Capacity for Backup Requirement

Battery Capacity for Backup Requirement

Calculate nominal battery capacity for a target backup duration from load, DoD and efficiency.

Updated September 2026

How it works

Calculate nominal battery capacity for a target backup duration from load, DoD and efficiency.

Formula:
Usable energy = load·hours; nominal capacity = usable energy/(DoD·η)·(1+reserve).

Before you use the result: Also check battery power, inverter surge, temperature, degradation, cycle life and safety.

Practical use

Use verified material data and project geometry. Treat results as planning estimates and compare them with the energy/thermal requirements that apply to the project.

Keep units consistent with the source information.
Use project-specific densities, pack sizes and coverage rates where provided.
Round purchasing quantities to supplier packaging and delivery rules.

How to use this calculator: Battery Capacity for Backup Requirement

Calculate nominal battery capacity for a target backup duration from load, DoD and efficiency.

Quick workflow

Enter the project values from the latest drawing, specification or verified site measurement.
Check units, material properties, allowances and any code- or supplier-specific parameters before calculating.
Review the result together with the formula, assumptions and the related checks shown on this page.

Worked example

Example inputs: Average backup load [kW]: 1.5; Required backup duration [h]: 8; Usable depth of discharge [%]: 90; System efficiency [%]: 92.

Using the sample values built into the calculator, the calculation gives approximately: Required usable battery energy: 12 kWh; Required nominal battery capacity: 15.94 kWh.

What the result means

Calculation method: Usable energy = load·hours; nominal capacity = usable energy/(DoD·η)·(1+reserve).

Before using the result: Also check battery power, inverter surge, temperature, degradation, cycle life and safety.

Common questions

What does this calculator do?

Calculate nominal battery capacity for a target backup duration from load, DoD and efficiency.

Which inputs should I verify?

Key inputs to verify include: Average backup load [kW], Required backup duration [h], Usable depth of discharge [%], System efficiency [%].

Can I use this result for final design or ordering?

Use the result as a transparent planning or checking aid. Final design, code compliance, supplier selection and project-specific decisions still need to be verified where applicable. Also check battery power, inverter surge, temperature, degradation, cycle life and safety.

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