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12V Battery Specifications

by David Sandoval

Nearly all car, motorcycle and tractor batteries are 12-volt, lead-acid batteries. These batteries can provide hundreds of amps of electrical current for a short period of time. This is why these batteries are commonly used in automotive applications.

Not all 12-volt, lead-acid batteries are interchangeable, however. It is important to consider the automobile's electrical requirements before attempting to install a 12-volt battery.

Battery Voltage

Even though most car, motorcycle and tractor batteries are sold as "12-volt" batteries, the nominal voltage of a fully charged battery is closer to 12.6 volts. The electrochemical reaction between the lead plates and the battery electrolyte is what produces the voltage differential between the positive and negative terminals on a battery. Over time, the lead plates within the battery will become covered with lead sulfate crystals. These crystals inhibit the electrochemical reaction between the lead plates and the electrolyte, causing a drop in battery voltage.

Electrical Current Capacity

The electrical current capacity for each battery is rated using two metrics: "cranking amps" and "cold cranking amps." Cranking amps are a measure of how much electrical current (as measured in amps) a battery can provide for 30 seconds at 32 degrees Fahrenheit. Cold cranking amps are a measure of how much electrical current a battery can provide for 30 seconds at 0 degrees Fahrenheit. Since the electrochemical processes that produce electrical energy in a battery are affected by cold temperatures, a battery will always produce more cranking amps than cold cranking amps.

Reserve Capacity

If the alternator (or generator in some older vehicles) fails, the battery is the sole source of electrical power for that vehicle. Batteries are designed to operate for several minutes in the event of an electrical failure.

A battery's "reserve capacity" is a measure of how long, in minutes, a battery can deliver 25 amperes of electrical current during a charging system failure.

About the Author

David Sandoval has served as a trainer and technical writer since 2000. He has written several articles online in the fields of home improvement, finance, electronics and science. Sandoval has an Associate of Applied Science in microelectronics from Northern New Mexico College.

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