Replacing a car battery is relatively easy and can be part of a regular auto maintenance schedule. While there seems to be a dizzying array of batteries on the market, only three companies produce most of the maintenance-free batteries used in the United States today -- Delphi, Exide and Johnson Controls Industries. Each company manufactures batteries that are marketed by different companies under different names. The name brand on the battery doesn't ultimately matter. What does matter is age, cold cranking amps, reserve capacity and group size.
- Age: Batteries usually come with a manufacture date on them, and they should be sold within six months of that date. Check the date carefully before you buy. The date is often coded. Most codes start with the letter indicating the month -- A for January, B for February and so on. The number indicates the year, as in 0 for 2000 or 1 for 2001.
- Group size: This measure determines the outside dimensions and where the battery terminals are. Make sure the group size of the battery you're buying matches that of the one you're replacing -- otherwise you could wind up with a battery that has a different size and configuration than your car can use. Fortunately, most battery sellers group them by the car make, model and year they can be used for.
- Cold cranking amps: This is a measure of a battery's capacity to start a car at 0 degrees Fahrenheit (-17 degrees Celsius), when the engine oil is thick and the battery's chemical potential is low. The higher the CCA, the better it will start in the cold. Most batteries list this on the battery sticker, though some only list CA, or cranking amps. CA is measured at 32 degrees Fahrenheit (0 degrees Celsius) and is usually a higher number. However, it gives a less accurate assessment of how well the car will start in the cold.
- Reserve capacity: This is the toughest number to find but one of the most useful. It indicates how long your car can run off battery power alone if the alternator suddenly dies. It can usually be found in the battery literature at the store or online, or occasionally on the battery itself.
Follow these rules and you should be able to weather the worst a bad battery can throw at you, and find a reliable new one when you need it.