Cover Story: Know Your Battery Terminology

Offering the customer several battery options is always a good idea, but answering the inevitable “what’s the difference” query takes a good knowledge of the basic performance measurements of automotive batteries. The two most important are cold cranking amperage, and reserve capacity:

COLD CRANKING AMPS

Cold cranking amperage is the ability of a battery to rotate and fire an engine in cold temperatures. The number represents the current in amperes (amps) that a fully charged battery can deliver for 30 continuous seconds at -18 C without dropping below 7.2 volts. Like money, more is better so higher CCA ratings represent the “better” battery if cold start is a customer concern.

CRANKING AMPS or MARINE CRANKING AMPS

A similar concept, but not quite the same. This rating refers to the current a fully charged battery can deliver at 0 C for 30 seconds without dropping below 7.2 volts (for a 12-volt battery). It’s a similar quantity, but be careful that you’re comparing “apples to apples” when it comes to cranking amperage, because no flooded lead acid battery will perform as well at -18 C as it will at 0 C.

RESERVE CAPACITY

Reserve Capacity is a rating that tells the consumer what’s left after the alternator or alternator belt fails. Technically, it’s the number of minutes a battery at 27 C can be discharged at 25 amps while maintaining a nominal voltage of 10.5 volts. Again more is better, but for a well maintained car or light truck, start with Cold Cranking Amperage before you introduce a concept like reserve capacity. After all, you’re replacing the belt BEFORE it breaks, right?