Automotive batteries are lead acid batteries which produce voltage and deliver current. They are made up of six cells, each producing 2.1 volts for a total full charge of 12.6 volts. Batteries are rated by cold cranking amps (CCA) which represent the current the battery can produce for 30 seconds at 0 degrees before the battery drops below 7.2 volts. The average rating for a battery today is about 500 CCA. The other battery rating is Reserve Capacity (RC). This measures the number of minutes that a battery at 80 degrees F can be discharged at 25 amps and maintain a voltage of 10.5 volts. The higher the RC rating, the longer the vehicle will operate if the alternator fails. If the vehicle sits for a number of days or a few weeks without being driven and the battery goes dead, this may be the result of a low reserve capacity battery.
Causes of premature battery failure are:
- Deep discharge (leaving lights on)
- Undercharging or loose alternator belt
- Excessive jarring or vibration due to loose or missing hold-down.
More than 30% of vehicles having batteries 3 years old or older experience battery failure. On average, batteries used in colder climates last longer than those used in warmer climates.