Many specifications and performance standards have been developed to evaluate batteries and measure their power. Several rating methods are used to provide the market, the consumer, and the seller with meaningful battery information. These rating methods are explained below.
COLD CRANKING AMPS (CCA)
The CCA rating represents in amps the current flow the battery can deliver for 30 seconds at 0o F. without dropping below 1.2 volts per cell (total of 7.2 volts for a 12-volt battery). The higher the number, the more amps it can deliver to crank an engine.
MARINE CRANKING AMPS (MCA)
Batteries designed for marine use may be rated at MCA instead of CCA. The MCA rating method measures battery output at 32o F., not 0o F. A battery's MCA rating will be one-third higher than its CCA rating would be.
To compare two batteries when one has an MCA rating and the other has a CCA rating. multiply the CCA rating by 1.3 for the equivalent MCA rating. Or, multiply the MCA rating by 0.77 for the equivalent CCA rating. Example:
500 CCA x 1.3 = 650 MCA
650 MCA x 0.77 = 500 CCA
The amount of reserve capacity represents the time in minutes a fully charged battery can deliver 25 amps at 80o F. without dropping below 1.75 volts per cell (total of 10.5 volts for a 12-volt battery). The reserve capacity rating defines the length of time a vehicle can be driven after its charging system fails while supplying power for ignition, lighting, and other accessories. The higher the number of minutes, the longer it will deliver 25 amps at 80o F.
The ampere-hour rating method is also called the 20-hour rating method. This rating represents the steady current flow the battery will deliver for 20 hours at 80o F. without dropping below 1.75 volts per cell (total of 10.5 volts for a 12-volt battery). For example, a battery that will continuously deliver 3 amps for 20 hours is rated as a 60 ampere-hour battery.
Most U.S. battery manufacturers now use the CCA rating method instead of the traditional ampere-hour rating method. Adding confusion. MCA ratings are beginning to appear on marine batteries. Be sure you know the difference between batteries.