How This Calculator Works
Battery Runtime turns the inputs into a visible formula-based estimate. Use the result as a planning check, then compare a lower, expected, and higher scenario when the input values are uncertain.
Use the battery runtime calculator to estimate how long a battery may power a device, appliance, inverter, or backup load.
The calculator converts amp-hours and voltage to watt-hours, applies usable depth and efficiency, then divides by load watts.
Formula
Runtime hours = Ah x volts x usable percent x efficiency / load watts.
Example Calculation
A 100 Ah 12 V battery has 1,200 Wh nominal. At 80% usable and 85% efficiency, a 150 W load runs about 5.4 hours.
When to Use This Calculator
- Estimate backup power
- Plan camping batteries
- Size inverter loads
Practical Scenarios
- Use the calculator before a decision depends on the number, then write down the inputs that would be easiest to verify. Use case: Estimate backup power.
- Rerun the estimate when the most uncertain input changes, so the result shows a useful range instead of one brittle answer. Start with Battery Runtime, then compare the changed result with the original.
- Use the related calculators when the result affects a wider cost, schedule, or planning workflow. This is especially useful when you need to size inverter loads.
Tips
- Battery ratings vary by discharge rate
- Inverters use power too
- Do not drain batteries beyond safe limits
Common Mistakes
- Confusing Ah with Wh
- Ignoring inverter efficiency
- Using peak watts instead of running watts
- Using one unusually good input as if it were the normal case.
- Mixing units, time periods, or assumptions from different scenarios.
Assumptions and Limitations
The Battery Runtime Calculator is most useful when every input belongs to the same real-world scenario, unit, and time period. Review the formula, assumptions, and related calculators before using the result in a decision.
- Local rules, fees, availability, timing, and real-world conditions can change the result.
- The result is an estimate and should be checked before making an important decision.
- Use realistic low, expected, and high scenarios when uncertainty matters.
Battery Runtime uses battery runtime, battery backup, amp hours and watt hours as the main context for the formula, example, and assumptions.
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