Peukert's law

Peukert's law is an empirical relationship between a battery’s discharge current and the time it can deliver current. It predicts lower usable capacity at higher discharge rates.

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Peukert equation: An empirical equation estimating battery discharge time from current, rated capacity, and a Peukert exponent. It expresses the law quantitatively and predicts runtime at a chosen current.
Battery runtime: The duration a battery can power a load before reaching a specified cutoff condition. Peukert’s law estimates how that duration changes when load current changes.
Ideal battery: A theoretical battery that maintains constant voltage and delivers its full rated charge regardless of load or discharge history. Unlike an ideal battery, real batteries often yield less usable capacity at higher current.
W. Peukert: A German scientist whose name is attached to an empirical rule relating lead–acid battery capacity to discharge rate. Peukert’s early battery tests gave the relationship its name.
Peukert exponent: A dimensionless exponent describing how strongly a battery’s available capacity falls as discharge current rises. Its value determines how sharply this law penalizes higher discharge rates.
Lead–acid battery: A rechargeable battery that uses lead-based electrodes and sulfuric acid electrolyte. The law is commonly applied to lead–acid batteries, whose usable capacity varies notably with discharge rate.
Coulomb counting: A method of estimating battery charge by integrating current entering or leaving the battery over time. Basic coulomb counting assumes charge changes track current, while Peukert’s law models rate-dependent usable capacity.
Battery testing: The measurement of electrical, mechanical, and safety performance under controlled battery conditions. The law emerged from discharge tests comparing runtimes at different currents.
Discharge rate: The rate at which electrical charge is removed from a battery, commonly expressed as current or C-rate. Peukert’s relationship uses discharge rate to estimate the resulting runtime.
Battery management system: An electronic system that monitors and controls a battery pack’s operation and safety. A battery-management system can use rate-dependent capacity models to improve remaining-runtime estimates.