Battery Runtime Calculator
Estimate battery runtime from rated energy, usable discharge, conversion efficiency, load power, and nominal DC voltage.
Runtime details
Use the battery's rated energy capacity. Do not enter a value that is already adjusted for the discharge window.
Estimated runtime
Runtime assumes constant load power and the entered discharge window and conversion efficiency.
About this calculator
Enter rated battery energy, the usable discharge window, overall conversion efficiency, load power, and nominal battery voltage. The calculator estimates delivered energy, runtime, and average DC battery current.
It does not size a battery system, confirm that an inverter can supply the load, or evaluate installation requirements.
Method and assumptions
Usable stored energy = rated capacity × usable discharge percentage. Estimated delivered energy = usable stored energy × conversion efficiency. Runtime = delivered energy ÷ load power. The displayed time rounds to the nearest minute and shows “Under 1 min” for shorter estimates.
Average battery input power = load power ÷ conversion efficiency. Average DC current = battery input power ÷ nominal battery voltage. The calculation assumes steady load and does not model changes in voltage, efficiency, or available capacity as the battery discharges.
Interpret the result
Use the result for an initial runtime estimate. Actual runtime depends on battery chemistry, discharge rate, temperature, age, inverter behavior, auxiliary loads, and battery-management limits.
FAQs
Should I enter rated or usable battery capacity?
Enter the rated energy capacity, then enter the usable discharge window separately. If the manufacturer only provides usable energy for your settings, use a 100% discharge window to avoid applying the limit twice.
What efficiency should I enter?
Enter the overall efficiency from battery DC energy to the load. Use a manufacturer value or measured system data when available. The example is editable and is not a product recommendation.
How should I interpret the battery current?
It is an average estimate based on load power, conversion efficiency, and nominal battery voltage. Battery voltage changes during discharge, so actual current can vary.
Does the result guarantee the battery can supply the load?
No. The calculator does not check continuous or surge power limits, inverter ratings, battery discharge ratings, temperature, wiring, protection, or equipment compatibility.
Sources
- U.S. Department of Energy, Solar Integration: Solar Energy and Storage Basics — battery energy and power concepts and system-level considerations.
- Use current battery and inverter documentation for rated energy, discharge limits, efficiency, voltage range, and continuous power.