Automotive batteries provide starting power for an automotive electrical system. It may be daunting, however, to try to purchase an automotive battery without knowing what to look for.
Many of the specifications can be confusing. It may not be readily apparent what reserve capacity is, or what the difference is between cranking amps and cold cranking amps. Once you understand what each specification means, choosing a battery becomes much simpler.
"Cranking amps" is a measure of a battery's capacity to provide electrical current at 00 degrees Celsius. This measurement represents how many amps of electrical current the battery can provide for 30 seconds before the battery voltage drops to 7.2 volts.
Cranking amps are also known as "marine cranking amps." The abbreviation for cranking amps is "CA;" the abbreviation for marine cranking amps is "MCA."
Cold Cranking Amps
"Cold cranking amps" is a measure of battery's capacity to provide electrical current at zero degrees Fahrenheit. This measurement represents how many amps of electrical current the battery can provide at that temperature for 30 seconds before the battery voltage drops to 7.2 volts. This number will always be lower than the cranking amps rating.
The abbreviation for cold cranking amps is "CCA."
Reserve capacity, or "RC", is a measure of how long a battery will provide electrical current. This measurement represents how many minutes (at 26.7 degrees Celsius) the battery can provide 25 amps of electrical current before the battery voltage drops to 10.5 volts.
In some countries, an additional rating is provided---the amp-hour. Amp-hours are a measurement of available electrical current for a period of time. For example, if a battery is rated at 40 amp-hours, the battery can provide 40 amps continuously for one hour, or one amp for 40 hours.
Month and Year Codes
Nearly all automotive batteries have two sets of consecutive numbers at the top of the battery. One row of numbers is meant to signify the last digit of the year the battery was purchased (such as "7" for 2007, or "9" for 2009). The other row is meant to signify the month of purchase.
Marking these numbers with a permanent marker often helps an automobile owner to see when the battery was purchased.