Though battery problems are often associated with cold weather, Consumer Reports magazine says heat is a bigger enemy of car batteries and will take a bigger toll on performance and reserve capacity. The magazine recommends that vehicle owners in hotter parts of the country have their car battery tested after two years of ownership and then every year after. Those who live in colder areas can wait four years to test performance and capacity, and then every year after."

Heat kills batteries," according to John Banta, a Consumer Reports project leader and part of the team that tests batteries for the magazine. "Many times in cold climates your battery fails to start your car on a below-freezing day. The reason this happens is that the heat of the past summers has weakened your battery. When you use it in the cold, the starter requires more electrical current to turn over the cold engine with its thickened oil."

Testing a battery's performance and reserve (or amp-hour) capacity is not just a matter of seeing whether it will hold a charge (or checking the electric eye found on some batteries to see if it is green), so testing is best done by an auto technician.