The Physics
Factbook
An encyclopedia of scientific essays

Energy of a Car Battery

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Bibliographic Entry Result
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Standardized
Result
Berger, John J. Charging Ahead: The Business of Renewable Energy and What it means for America. Canada: Fitzhenry & Whiteside Ltd., 1997: 287. "But today's lead-acid batteries have only about 30 watt-hours of energy per kilogram, and need to be replaced every two or three years, or after as few as 15,000-20,000 miles." 0.6โ€“7.3 MJ
Sonnenschein Prevailer Dryfit German DF Series SLA GEL Batteries. Battery Web. [see below] 2.1โ€“8.6 MJ
Optima Batteries. Battery Web. [see below] 2.1โ€“4.8 MJ

A battery is a device that converts chemical energy into electrical energy. A dry-cell flashlight battery consists of an electric cell, but larger batteries are made up of a group of cells that are connected to act as a source of direct electric at a given voltage. A cell consists of two dissimilar substances, a positive electrode and a negative electrode, that conduct electricity, and a third substance, an electrolyte, that acts chemically on the electrodes. A group of several such cells connected together is called a battery. Batteries are widely used as a source of direct current electrical energy in automobiles, boats, aircraft, portable electric and electronic equipment, and lightning. A car battery is used mainly to start the motor. Once the motor is running, an alternator supplies current to recharge the battery. A few car battery companies include Diehard and Trojan.

The formula for determining battery energy is:

E = P·t = V·I·t

Where

I = Current Expressed in amperes
V = Electromotive force expressed in volts
P = Power expressed in watts
t = Time expressed in hours
E = Energy in joule

For Car Batteries:

Source: Sonnenschein Prevailer Dryfit German DF Series SLA GEL Batteries. Battery Web.

Model Volts Ah at 20 hours Weight (lb.)
DF115 12 50 39
DF125 12 55 42
DF150 12 50 51
DF180 12 85 66
DF230 12 110 82
DF25 12 15 13
DF45 12 30 23
DF4D 12 165 106
DF4DLT 12 95 86
DF6V180 6 200 67
DF75 12 42 27
DF8D 12 200 150

DF115: (50 Ah) x (12 V) x (3600 s) = 2,160,000 J
DF180: (85 Ah) x (12 V) x (3600 s) = 3,678,000 J
DF8D: (200 Ah) x (12 V) x (3600 s) = 8,640,000 J

Source: Optima Batteries. Battery Web.

Model Volts Ah Weight (lb.)
34/78/800U 12 50 39
34/800S 12 50 38
34M/1000M 12 50 39
6V/850/6 6 50 19
75/35-925 12 44 34
D34/78/D750U 12 55 44
D34/D750S 12 55 43
D34M/D900M 12 55 44
D6V/D750/6 6 50 24
R34/800R 12 50 38
TF 12 110 90

34/800S: (50 Ah) x (12 V) x (3600 s) = 2,160,000 J
D34/D750S: (55 Ah) x (12 V) x (3600 s) = 2,376,000 J
TF: (110 Ah) x (12 V) x (3600 s) = 4,752,000 J

Raymond Tran -- 2002