Formula
- Use the units shown beside each field.
- Results update automatically whenever you change an input.
- Displayed values use up to four decimal places, or scientific notation for very small or large numbers. Calculations use standard floating-point arithmetic; exact integer and fraction tools identify their own precision rules.
- Nominal-energy model. No Peukert effect, aging, cutoff-voltage or load variation model.
Example Calculation
- Nominal voltage: 12 V
- Capacity: 100 Ah
- Usable capacity: 80 %
- Conversion efficiency: 90 %
- Constant load: 120 W
12 V × 100 Ah, 80% usable capacity and 90% efficiency can supply 120 W for an estimated 7.2 hours.
Frequently asked questions
How do I use this calculator?
Enter nominal voltage, capacity, usable capacity, conversion efficiency, constant load. The result updates automatically. Use Reset to restore the example values.
What method does it use?
runtime=voltage × Ah × usable fraction × efficiency / watts.. Nominal-energy model. No Peukert effect, aging, cutoff-voltage or load variation model.
Why might a rounded result differ?
The calculation keeps full numeric precision internally, then rounds the displayed result. Rounding intermediate steps by hand can produce a slightly different answer.
Are my inputs saved online?
No. This calculator processes your inputs in your browser. A recently used list stores only calculator names on this device, not your entered values.
Check the assumptions and units before using this result. Read about calculation methods.