When to use this calculator
Estimate runtime from nominal battery energy, usable fraction and load power. Assumes constant load and capacity. Real battery characteristics can change runtime.
Explore the dc circuits & components calculators for other questions in this topic. For a related calculation, use the Battery Series Voltage Calculator: Find the nominal voltage sum for identical battery units in series.
PUTTING IT INTO PRACTICE
Battery Runtime: a worked example
The values below are an illustrative example, not a recommendation. Replace them with measurements or assumptions that match your question.
| Input | Example value |
|---|---|
| Nominal voltage (V) | 12 |
| Capacity (Ah) | 200 |
| Usable energy (%) | 80 |
| Conversion efficiency (%) | 90 |
| Load power (W) | 300 |
| Result | 5.76 hours |
- Check the input labels and enter the example values above.
- Apply the relationship: Hours = V × Ah × usable/100 × efficiency/100 ÷ watts.
- The result is 5.76 hours, rounded for display.
How to interpret your result
Assumes constant load and capacity. Real battery characteristics can change runtime.
Ideal component models omit tolerances, heat and parasitic effects. Distinguish nominal energy from usable energy for batteries. Component ratings and installation requirements need separate manufacturer and design checks.
Frequently asked questions
Can these calculations select a safe installation rating?
No. They explain ideal relationships and do not include every thermal, protective or regulatory requirement.
How do I use the battery runtime calculator?
Enter nominal voltage (v), capacity (ah), usable energy (%), conversion efficiency (%), load power (w). The result updates automatically. Use the units shown beside each input; the example values illustrate the method.
Which formula does this calculator use?
Hours = V × Ah × usable/100 × efficiency/100 ÷ watts.
What should I check before using the result?
Assumes constant load and capacity. Real battery characteristics can change runtime.
How are results rounded?
Scalar numbers display up to six decimal places, with scientific notation for very large or small values. Text, fraction, date and schedule outputs use the format described on the tool. Intermediate calculations use JavaScript floating-point arithmetic. Keep sensible precision for your measurements.
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