Capacity Peukert numbers

The efficiency factor of a discharging battery is expressed by the Peukert s law. W. Peukert, a German scientist (1897), devised a formula expressing loss at a given discharge rate in Peukert numbers. Because of the sluggish behavior of lead acid, Peukert numbers apply mostly to this chemistry. They help to calculate the capacity under various load conditions. 

FIGURE 8.3 Available capacity of a lead-acid battery at Peukert numbers of 1.08 to 1.50. A value close to 1 has the smallest losses higher numhers deliver lower capacities. (Source von Wentzel [2008].)... 

This energy is measured not only in Joules (1 J = 1 W s) but also in watt-hours (1 Wh = 3600 J.). Both the maximum ampere-hour capacity and the watt-hour energy depend on the amount of reactants in a battery at the start of discharge. As the discharge current increases, both the discharge voltage and the reactant utilization coefficient diminish. A number of attempts to find a relationship between the actual battery capacity and the discharge current were reported. An approximation found in 1897 by Peukert for lead acid batteries is sometimes used ... 

The Peukert law takes into account the internal resistance and recovery rate of a battery. A value close to 1 indicates a well-performing battery with good efficiency and minimal loss a higher number reflects a less efficient battery. Figure 8.3 illustrates the available capacity as a function of ampere with different Peukert ratings. 

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