The Physics
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Power of a Car Battery

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Muller, Richard A. Batteries. Lawrence Berkeley National Laboratory.
voltage 12 volts
cold cranking amperes 800 amps (at 7.2 volts)
reserve capacity 120 minutes = 7,200 seconds (at 10.2 volts)
9600 W
Product Informations. "Cold Cranking amps — 660 A" 4750 W
Starting Batteries. "Most common cars require relatively low cranking amps. They usually take 400 to 600 cranking amp batteries. Sport utility vehicles and light trucks usually require higher cranking amps in the 700 to 1000 range" 4320 W
Vertex Sealed Racing Batteries. Taylor Vertex. "526 cold cranking amps" 3790 W
Chevrolet Cavalier 2 door Coupe — Vehicle Specifications. ChevroletCarPrices. "Cold Cranking amps @ 0 °F — 600" 4320 W

A car battery is a plastic box divided into six cells that is filled with an electrically conductive sulfuric acid solution called an electrolyte. This chemical interacts with the battery's electrodes, or metal plates containing lead and lead oxide, to produce 12 volts of electricity.

The car battery has three basic tasks. First, it provides the initial power to start the engine of a car. Second, it keeps itself recharged and generates power when the car's engine is not running. Lastly, it can maintain a low current to power the lights, horn and other electrical devices for a short period.

The rating used to define a battery's ability to start an engine in cold temperatures is called Cold Cranking Amperage (CCA). The CCA of an auto battery is the amount of current a given battery can deliver for 30 seconds at 0 °F (−18 °C) without dropping below 7.2 volts for a 12 volt battery. To find the power of a car battery we multiply the CCA number by 7.2 volts. For example,


P = IV
P = (600 A)(7.2 V)
P = 4320 W

Most modern cars require relatively low cold cranking amps that range from 400 to 600. Sports cars and light trucks require higher cranking amps ranging from 700 to 1000 A.

Melissa Ng -- 2001