Peukert's Equation

The table below may be used to understand the effect of high rates of discharge on available battery capacity. It may also be used to estimate the exponent "n" for a battery after a single discharge test. The table is based on a 100-Ah battery but may be used for any capacity battery by using an appropriately scaled current. See the examples below:

EXPONENT

PERCENTAGE OF AVAILABLE CAPACITY FROM A 100 Ah BATTERY AT DIFFERENT DISCHARGE RATES USING DIFFERENT PEUKERT'S EXPONENTS

 

 

 

DISCHARGE RATE IN AMPS

 

 

n

5

10 16.7

25

50

75

100

150

200

250

300

400 500

1100 100 100 100 100 100 100 100 100 100 100 100 100

1.1

100

93

88

85

79

76

74

71

69

67

66

64

63

1.2

100

87

78

72

63

58

55

51

48

46

44

42

40

1.25

100

84

74

67

56

51

47

42

40

37

36

33

32

1.3

100

81

69

62

50

44

41

36

33

31

30

27

25

1.4

100

76

61

52

40

34

30

26

23

21

20

17

16

1.5

100

71

55

45

32

26

22

18

16

14

13

11

10

Example#1:Supposeyouhavea200 Ah

Example #2: A 100 Ah battery

battery. Now discharge at a 50-amp

with a Peukert's exponent of 1.3

rate until the battery reaches 1.75 V

will deliver only 41% of its

per cell (10.5 V for a 12 V battery).

capacity when supplying a 100-

This would be equivalent to a discharge

amp load.

rate of 25 A for a 100 Ah battery. If the

 

battery delivered 67% (134 Ah) the

 

appropriate Peukert's exponent would

 

be 1.25.

 

40