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http://en.wikipedia.org/wiki/Peukert%27s_law

All text is available under the terms of the GNU Free Documentation License: http://en.wikipedia.org/wiki/Wikipedia:Text_of_the_GNU_Free_Documentation_License

# Peukert's law

Peukert's Law, presented by the German scientist W. Peukert in 1897, expresses the capacity of a battery in terms of the rate at which it is discharged. As the rate increases, the battery's capacity decreases, although its actual capacity tends to remain fairly constant.

Peukert's law is as follows:

$C_p = I^k t \,$

where:

• $C_p \,$ is the capacity according to Peukert, at a one-ampere discharge rate, expressed in A·h.
• $I \,$ is the discharge current, expressed in A.
• $k \,$ is the Peukert constant, dimensionless.
• $t \,$ is the time of discharge, expressed in h.

For an ideal battery, the constant k would equal one, in this case the actual capacity would be independent of the current. For a lead-acid battery, the value of k is typically between 1.1 and 1.2 however. The Peukert constant varies according to the age of the battery.

The Peukert law becomes a key issue in a battery electric vehicle where batteries rated at 20 hour discharges are used at much greater rates of about 1 hour.

Watt-hour counters can be programmed with battery capacity, Peukerts exponent, and other particular batteries characteristics. They then count watt-hours and can display various information relating to the state of charge of the battery pack, including remaining energy and thus range.

## References

• W. Peukert, Über die Abhängigkeit der Kapacität von der Entladestromstärcke bei Bleiakkumulatoren, Elektrotechnische Zeitschrift 20 (1897)
• D. Doerffel, S.A. Sharkh, A critical review of using the Peukert equation for determining the remaining capacity of lead-acid and lithium-ion batteries, Journal of Power Sources, 155 (2006) 395–400

• IEEE Paper on Lead batteries
• Peukerts for LI-Poly [1] - EVDL
• Charging and Peukert effect question - EVDL
• Peukert's equation answers from a battery engineer, Part 1 - EVDL
• Peukert's equation answers from a battery engineer, Part 2 - EVDL
• Peukert's equation answers from a battery engineer, Part 3 - EVDL
• Question about Peukert Exponent - EVDL
• Clarify Peukert effect - EVDL
• A fully detailed explanation of Peukert's effect - By Chris Gibson, designer of battery monitoring equipment
• A Peukert spreadsheet in Microsoft Excel format - Again by Chris Gibson