What this tool helps you organize
Estimate an idealized lamp duration from stored energy. It is one defined worksheet, not a complete assessment of your circumstances.
No actual battery-health, charging, thermal or electrical-safety assessment.
Method and calculation rules
Usable Wh = rated energy × factor/100. Runtime = usable Wh/lamp W. Nights = runtime/hours per night.
Display values are rounded for readability. The calculation uses the entered numbers before display rounding. Whole-unit outputs use the rounding rule stated in the method.
Know your inputs
- Rated stored energy (Wh) — Accepted range: 0.01 to 1000000.
- Chosen usable-energy factor (%) — Accepted range: 0 to 100.
- Lamp draw (W) — Accepted range: 0.01 to 1000000.
- Use per night (h) — Accepted range: 0.01 to 24.
A worked example
Illustrative inputs: Rated stored energy (Wh): 74; Chosen usable-energy factor (%): 85; Lamp draw (W): 4; Use per night (h): 3.
Usable energy: 62.9 Wh
Lighting hours: 15.73 h
Nights at entered use: 5.24
These sample figures illustrate the formula, not a recommended target or a prediction.
How to use the working copy
Define a single scenario, check the units and replace each sample value that does not match it. Calculate and read all three result components, not just the most favorable number.
Change one assumption to compare scenarios. An edited field makes the previous answer stale; recalculate before downloading or printing. Reset sample clears the open result and restores the example entries.
What the answer cannot establish
No actual battery-health, charging, thermal or electrical-safety assessment.
The tool does not verify the accuracy, completeness or current validity of your inputs. Use authoritative current information and qualified judgement when the decision requires them.
Questions about this worksheet
Are the starting values a suggested target?
No. They show how the arithmetic behaves. Use your own checked values and do not infer a recommendation.
Why is my previous result marked stale?
Changing an input means the displayed answer no longer describes the current fields. Recalculate to refresh it.
Can I share an export?
Review the entries and limitations first. A downloaded file is a working copy, not an independently verified report.
Your entries and privacy
The bundled calculation runs in this open browser page. Inputs are not automatically saved as a server-side calculation history. Browser refresh or navigation may clear them.
Contact messages and technical website records are separate from calculator arithmetic. Read the Privacy Policy for the distinction; do not enter confidential records or credentials.