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The secret life of batteries

If you take a look under the hood, you might gain a new appreciation for your hard-working battery.

Like produce, batteries are best bought fresh—you want one that was manufactured less than six months ago. Look for a two-character code stamped into the top or side of the battery, or printed on the label. For most manufacturers, the letter in this code indicates the month of manufacture and the number indicates the year. The letters go from A to M, leaving out I. For example, G8 means July 2008. A few makers use a different code. Before purchasing, ask the seller to explain the date code if you are unsure.

Lead-acid batteries typically last from three to five years. Their lifespan is shortened by driving habits, extreme weather, lack of maintenance and the number of aftermarket accessories the battery must support. Make a habit of turning off any add-on media players, navigation systems or other devices before you shut down the engine.

Automotive batteries last longest when maintained at or near a full state of charge. If your vehicle will sit idle for more than a few weeks, invest in a battery tender to keep the battery fully charged.

During freezing conditions, a battery may lose as much as a third of its power. However, hot weather is just as bad, weakening internal battery components, evaporating critical fluids and contributing to overcharging. The average battery life in hot climates is just 3½ years.

Proper care and cleaning can increase a battery's longevity. As part of routine maintenance, clean any corrosion from the battery terminals, case, brackets and the tray that holds the battery. Tighten loose cables and brackets. Replace worn alternator drive belts—these diminish the system's ability to recharge the battery.

Even with good habits on your side, all batteries eventually wear out. Quite often a battery will signal its impending demise with one or more of these warning signs:

  • The starter motor may crank the engine more slowly than usual.


  • There may be a grinding, clicking or buzzing noise when turning on the ignition.


  • Headlights may dim when the vehicle is idling, but brighten when the engine is revved.

Any of these symptoms are a good sign that it's time to have your battery checked. Visit www.AAA.com and click on "Automotive" for more car care tips and information about the AAA Mobile Battery Service testing program.