Share:
How It Works
Peukert's Law models how a battery's usable capacity drops as you draw more current. The formula T = C / In accounts for internal losses that worsen at higher discharge rates. An ideal battery has a Peukert number of 1, but real-world lead-acid batteries typically fall between 1.1 and 1.3.
Example Problem
A 100 Ah lead-acid battery with a Peukert number of 1.2 is discharged at 10 A. How long will it last?
- Calculate In: 101.2 ≈ 15.85
- Apply the formula: T = 100 / 15.85 ≈ 6.31 hours
Without the Peukert correction (n = 1) the answer would be 10 hours, so the real runtime is about 37% shorter at this discharge rate.
Frequently Asked Questions
What is the Peukert number for lithium batteries?
Lithium-ion batteries have a Peukert number very close to 1.0 (typically 1.0–1.05), meaning their capacity stays nearly constant regardless of discharge rate. That is one reason lithium batteries outperform lead-acid in high-drain applications.
How do I find my battery Peukert number?
Discharge the battery at two different constant currents and record the times. Then use the Peukert number solver above with the known capacity. Most manufacturers publish this value in the battery datasheet.
Does temperature affect battery discharge time?
Yes. Cold temperatures increase internal resistance and reduce effective capacity. A 100 Ah battery at 0°C may deliver only 70–80 Ah. Always factor in temperature when sizing batteries for outdoor or winter applications.
Related Calculators
- Lightning Distance Calculator — estimate storm distance from the flash-to-thunder delay.
- Percent Difference Calculator — compare two battery test results side by side.
- Ohm's Law Calculator — solve for voltage, current, resistance, or power in circuits.
- Days Between Dates Calculator — count days between two dates for charge cycle tracking.
- Energy Converter — convert between watt-hours, joules, and other energy units.