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Enter your values, then click Calculate result.How this calculator helps
This global battery run time calculator models energy available to a constant electrical load. It separates nominal capacity, usable fraction and conversion losses instead of hiding one universal efficiency. Ah and Wh input modes share one canonical page. Pakistan backup and sizing tools remain unchanged; this worksheet serves a general constant-load energy task with explicit assumptions rather than electricity-bill pricing, solar yield or a battery chemistry recommendation. The result is an energy estimate, not a guaranteed outage duration.
How to use it
- 1
Enter the complete battery-bank nominal voltage and choose Ah or Wh capacity.
- 2
Enter the usable fraction and conversion efficiency from your documented scenario.
- 3
Supply constant real output watts and click Calculate result.
- 4
Review nominal energy, usable load energy and modeled hours together; compare several measured load cases.
Formula and methodology
Nominal Wh = volts × Ah, or supplied Wh. Usable load Wh = nominal Wh × usable fraction × conversion efficiency. Runtime hours = usable load Wh / load watts.
The calculator applies the displayed arithmetic to the values entered on this device. It does not silently load a local tax rate, currency conversion or commercial assumption.
Worked calculation example
A 12 V, 100 Ah battery has a nominal 1,200 Wh rating. With a supplied usable fraction of 80% and conversion efficiency of 90%, 864 Wh reaches the load in this model. A constant 120 W output then lasts 7.2 hours, or 432 minutes. Entering 1,200 Wh directly gives the same energy result. The approximate battery-side current is 120/(12 × 0.9), or 11.111 A, not simply 120/12 when losses are included.
How to interpret your result
Runtime is the duration for which the supplied usable load energy would support the supplied constant watts. It should be read with both percentage reductions, because omitting either can materially change the estimate. The current output provides a separate approximate battery-side demand; it does not establish that the bank, cables or converter can safely supply that demand.
For different inputs or formulas, use Watt Hour Calculator; Electricity Usage Calculator; Ohms Law Calculator.
Related questions this calculator covers
- battery run time calculator
Scenario comparison
| Scenario | What it shows |
|---|---|
| Double load | the modeled hours halve with all energy inputs unchanged. |
| Ah/Wh equivalence | 12 V × 100 Ah matches a supplied 1,200 Wh rating. |
| Zero load | rejected because dividing by no demand gives no finite runtime. |
Common mistakes to avoid
- Treating Ah as Wh.
- Applying the same capacity reserve twice.
- Using VA as real watts without checking power factor.
Calculate nominal Wh by hand, apply each fraction once and divide by the watts. Convert the result to minutes by multiplying by sixty. Repeat in the alternative capacity mode and confirm the same result. Check a measured runtime against the actual capacity and load conditions instead of assuming every discrepancy is a software error.
Authoritative reference. Method reference checked for this worksheet. The calculation and examples are independently implemented; read the specific scope and units above.What can affect the result?
Ah and Wh are different ratings
Amp-hours describe charge capacity at a stated rating condition. Watt-hours describe energy. To turn Ah into nominal Wh, multiply by the battery system nominal voltage. Do not multiply a Wh rating by voltage again. Milliamp-hours require division by one thousand before entering Ah. Series and parallel battery arrangements affect bank voltage and Ah differently; use the complete bank rating rather than adding every label without considering wiring.
Capacity usable at the load
The usable fraction is an independently chosen scenario input. It can account for the portion of nominal storage available before a specified cutoff, reserve or other documented limitation. The calculator does not infer a safe discharge percentage from a battery name. If a manufacturer already rates usable output Wh, applying another reserve may double-count the adjustment. Record what the original capacity rating means and which reductions have already been included.
Conversion efficiency
Conversion efficiency represents the share of usable battery energy delivered through the relevant electronics to the output load. It is entered as a percentage, not assumed from a brand. Efficiency may change with load and temperature; one constant input summarizes a scenario. Do not include the same loss in both the battery capacity and efficiency field. Idle consumption, if relevant, should be included in the constant load rather than ignored.
Choose a realistic power draw
Use average real watts for the observation interval, not the maximum nameplate wattage unless that is the planned constant demand. A refrigerator, motor or computer can have changing loads and startup behavior. The simple worksheet does not simulate duty cycles, surges or protection trips. For a varying pattern, estimate an independently justified average and compare several cases. Apparent VA and true watts are not interchangeable without an appropriate power-factor basis.
Why a real battery can differ
Actual delivered capacity depends on discharge rate, age, temperature, cutoff settings, chemistry and the manufacturer test condition. An Ah label alone does not predict those effects. This model does not implement Peukert curves, cell balancing, charging time or inverter compatibility. The battery-side current is an approximate constant-voltage calculation; actual current changes as terminal voltage changes. Treat the displayed precision as arithmetic, not a laboratory discharge measurement.
Verification and planning
Check volts and capacity against the same battery-bank specification and test the actual equipment through a suitable safe operating procedure. Higher load must reduce modeled runtime, while higher available energy must increase it. Doubling the load halves this constant-energy estimate. Do not use the result to approve wiring, cell arrangements, protective devices or discharge limits. Those depend on manufacturer instructions and the applicable electrical requirements.
Privacy and browser processing
Values entered on this page are processed in the current browser session. SolvePilot does not require an account and does not receive the values entered into the calculator. Refreshing or closing the page clears the working values unless the browser itself restores a previous session. Avoid entering identifying or account information because the calculation needs summary values only.
Accuracy and verification
Accuracy depends first on input quality. Confirm definitions, scales, dates and source information before entering a value. Keep an independent record of any result used for planning because this page does not create an official statement or retain a calculation history.
Limits of this estimate
Use only the disclosed input domains and model. Treating Ah as Wh. Review the method-specific boundaries above and the linked source before interpreting a result. Calculations use browser floating-point arithmetic; displayed digits are not a measure of real-world certainty. Your entries stay on this device and are not submitted to a calculation server.
Sources and review information
Frequently asked questions
Can I use mAh?＋
Convert mAh to Ah by dividing by 1,000, then use the correct nominal voltage.
Why do I enter voltage in Wh mode?＋
Stored energy comes directly from Wh. Voltage is used only for the approximate battery-side current output.
Does this model lead-acid discharge curves?＋
No. It is a constant-energy estimate and does not implement chemistry-specific discharge curves.
Is efficiency a fixed 90%?＋
No. Ninety percent is a demonstration input; supply the efficiency appropriate to your scenario.
Can it approve my inverter or battery setup?＋
No. Compatibility, surge capability and protective design require manufacturer specifications and appropriate electrical review.