How the runtime estimate works.
The calculator is a simple planning model that helps you explore how battery capacity and a steady device load relate. It is not a test of a specific battery or appliance.
Formula
The editable default factor is 77%, formed as a simple illustrative combination of 85% usable capacity and 90% AC inverter efficiency. Battery chemistry, controls, output type and operating conditions vary. Replace this default with model-specific manufacturer information where available.
Example device loads
The sample values—such as a 100 W cycling-average refrigerator estimate and a 12 W router—are broad illustrations for demonstrating the math. They are not universal appliance specifications. Actual draw varies substantially by model, age, settings, ambient conditions and duty cycle. Use a plug-in power meter, appliance documentation, or a qualified professional where appropriate.
What the model leaves out
- Motor startup surge and maximum continuous output.
- Changes in appliance duty cycle or power use over time.
- Battery reserve, aging, temperature, degradation and device protection cutoffs.
- Different efficiency across AC, DC and USB outputs.
- Charge time, solar variability, and interactions between simultaneous loads.
Before buying, check both watt-hour capacity and rated/surge output in the product manual. This estimate is educational, not a guarantee, quote or safety assessment.
Sources and update practice
We link to official safety and consumer guidance in relevant pages and prefer equipment manuals for device-specific ratings. Our methods page is dated and will be revised when the tool or its assumptions materially change. Contact us with a correction.