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5 things you should know about car batteries

Hands of car mechanic using cables to start a car engine. panoramic banner How long your battery lasts depends, in large part, on where you drive and the age of your car. | Photo by thodonal/

How long a battery should last is an excellent question, but a difficult one to answer. Batteries in desert climates can fail in two years, and some batteries that are 5 or 6 years old work just fine. It’s hard to be more precise, because a variety of factors affect a battery’s performance and life span.

They do more than start the car

In the old days, a battery’s primary function was to start the engine. While that’s still true, since cars are now loaded to their rooftops with vast numbers of electronic doodads, the battery also must work hard to keep those things functioning.

For example, even when the engine isn’t running and the alternator isn’t charging the battery, it must keep things like the radio presets and the security alarm operational. And many new cars come with a fuel-saving start-stop feature that causes the engine to automatically turn off and restart perhaps dozens of times during a single trip, relying on the battery each time.

Today’s batteries are better

Fortunately, batteries have improved since the days when they needed periodic topping-off with distilled water. Today, a battery is typically “maintenance-free”—sealed and meant to retain its electrolyte solution for its lifetime. And now there’s an alternative to the traditional lead-acid battery: AGM (absorbent glass mat) batteries are coming as original equipment on many new cars. They’re generally more robust, although they’re also more costly.

Charge it!

A car battery must be kept well charged. Not only will this ensure that the car starts when you need it to, but the battery will have a longer life span. Your car’s battery may have a circular charge-indicator “eye” on its top. If the eye is green, the battery should be in a full state of charge. If it’s another color or clear, let your service rep or tech know.

Lead-acid batteries in particular are damaged by deep discharges. Some things that can cause excessive drain and shorten battery life are:

  • A malfunction (a stuck fuel-pump relay, for example) or an electronic device, such as a cell phone, left plugged into an “always on” power receptacle overnight.
  • Undercharging from, say, a faulty alternator or too many short trips that don’t give the alternator time to recharge the battery.
  • Summer heat of 100-plus degrees, which increases a battery’s internal discharge. Extreme cold also negatively affects battery chemistry.

Use it or lose it

A battery will slowly drain and eventually die during a long period of inactivity. If you drive your car infrequently—say, less than once every two weeks—a trickle charger that monitors the state of charge and recharges the battery when necessary is a good investment. They’re available from various retailers, auto-parts stores, and online.

Every few months, check to be sure the battery is securely mounted on its platform, that the cable clamps are tightly secured, and the terminals are clean. If the terminals are corroded, have your service facility clean them, because disconnecting a battery without providing an alternative power source can create havoc in modern cars. The absence of battery-supplied voltage erases the memories of modules that control the transmission, antilock brakes, and other components.

If your car’s battery is 3 to 4 years old, have a technician load-test it. If it can no longer hold a proper charge, be sure to buy a replacement battery that’s the correct fit and matches or exceeds the cold-cranking amps and reserve-capacity ratings of the original. If the battery is 5 years old or older, consider replacing it. Think twice before installing the replacement yourself, however, for the same reason mentioned above—your vehicle might need diagnostic scanning and reprogramming before some of its components will work right.

Use care when jumping a dead battery

And beware of jump-starting a car with a dead battery. Electronic systems on modern vehicles are at risk of damage from electrical surges and voltage spikes, and jump-starting adds to the risk. You might damage a critical component that could be expensive to replace.

If you must jump-start a battery yourself, follow the directions in your car’s owner’s manual to the letter. It’s much better, however, to have professionals—like AAA Roadside Assistance—do the job.

And if your battery should fail unexpectedly, the AAA Mobile Battery Service can come to you to test your battery and install a new one if needed. All AAA batteries come with a nationwide, 3-year free replacement. AAA will also recycle your old battery.

AAA Automotive Correspondent Peter Bohr has been writing about cars for more than four decades.

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