Question Of The Day: Why Does My Car Battery Keep Dying?

Question: Why does my car battery not last very long?

A battery is definitely not the sexiest item on a car. In fact, it’s safe to say that very few people ever inquire about these little black boxes when researching their next vehicle purchase. However, a car with the best gas mileage, the fanciest safety features, and the most exotic hood ornament won’t even make it off the lot if the battery doesn’t work—which arguably makes it the most important aspect of the car.

“A car battery works exactly the same as any other battery,” says Richard Reina, product trainer at “The battery has a ‘positive’ terminal and a ‘negative’ terminal, and electrons flow through wires from one terminal to the other.” The primary function of a car battery is to start the engine by powering the starter motor and provide electric power to the spark plugs to ignite the fuel. It also provides electric power to the lights, horn, heater, etc.

That’s an awful lot of responsibility for a 12-volt battery—the voltage used on most modern vehicles, especially considering that the batteries in your household flashlight supply a whopping 1.5 volts of electricity. And just like your typical flashlight, camera, and smoke detector batteries, car batteries eventually wear out and need to be changed from time to time. “An average battery [life] will be in the 3-4 year range,” says Bob Augustine, technical training manager for Christian Brothers Automotive. But that life can be dramatically shortened depending on how you treat your car:

Extreme Temperatures: “Extreme cold and/or heat stress the internal chemistry of the battery and induce premature failure,” continues Augustine. And the definition of “extreme” might not be as far-reaching as you think. The temperature need only creep above 100°F or run below 10°F to result in very bad news for your car. It turns out that car batteries eventually experience battery sulfation, a build-up of lead sulfate crystals. And leaving your car in extreme conditions will speed up the process. “This sulfation can shorten the life of the battery and lengthen the amount of time needed to charge the battery,” says Augustine.  

Faulty Charging System: It’s the responsibility of the alternator/generator to keep the battery charged. But if it provides a charge that’s too high or too low, then you have a problem. “The battery is 12.6V DC when fully charged, so the alternator/generator creates a voltage between 13.4V-14.7V DC to maintain a correct state of charge based on the electrical load,” says Augustine. If the battery is being under or over charged the culprit could be anything from mechanical flaws — a loose connection, a bad circuit, a faulty alternator — to driver error, such as forgetting to turn off the lights.

Short-Term Driving: Driving your car too often can contribute to a short battery life, but the number of miles driven isn’t nearly as important as how they were accumulated in the first place. “Many short drives will lessen the life of a battery faster than a few long trips,” says Reina. This is because “the most taxing use of the battery in your vehicle is the initial engine start.” And keep in mind that while the ignition is requiring this extra burst of power from the battery, the alternator hasn’t even started the recharging process, which is time consuming and usually occurs while you drive.

Keeping up with your car’s regular maintenance schedule is the best way to prevent having to shell out too much cash for car batteries. Losing a battery once a year for three years indicates something off in the electrical system; it could be as simple as a glovebox light that stays on even when the door’s closed. The auto pros will be able to spot any encroaching issues surrounding the battery and nip them in the bud.

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