There is no simple answer, but based on decades of industry experience, we know that three key factors affect the life of a car battery: time, heat and vibration.
Batteries gradually deteriorate until they can no longer provide enough power to start an engine. This wear time could take three to five years and a vehicle's usage pattern is one factor contributing to the rate at which a battery will age. Batteries in cars driven mostly on short trips may not fully recharge and batteries in vehicles parked for extended periods naturally self-discharge. In either case, using a maintenance charger like AAA's Battery Tender will keep the car battery fully charged and extend its service life.
Heat facilitates the chemical reaction car batteries use to generate electricity, but it also increases the rate of battery degradation. In cooler northern climates, a battery may last five years or longer, but in hot southern locales, a car battery will typically last approximately three years.
Batteries reside in a harsh under-the-hood environment where temperatures can easily exceed 200 degrees Fahrenheit in hot weather. To combat this heat, automakers may mount the battery in an isolated area, install a heat shield over the battery, or relocate the battery outside the engine compartment, often under the back seat or trunk floor.
Vibration causes internal battery parts to break down. To minimize vibration effects, use special hold down hardware to secure the battery in place and prevent it from moving. Missing or loose hold down hardware can significantly shorten battery life.
While less common than the aforementioned factors, a malfunctioning charging system will also reduce battery life. Persistent under- or over-charging accelerates battery aging. Some newer cars with absorbent glass mat (AGM) batteries require careful control of charging rates for maximum battery life, and the automaker may even alter the charging strategy as the battery ages. Finally, allowing any car battery to go completely dead will take a big chunk out of its lifespan, even if you can recharge and put the dead battery back in service.
You may have a battery problem if the starter motor cranks the engine slowly or the Battery/Charging warning lamp illuminates on the dashboard. In older models, dim incandescent headlights, particularly when the car is idling, indicates a weak battery.
Not every failing battery reveals itself through obvious symptoms so take precautions to avoid a dead battery situation. Inspect the car battery at every oil change. Make sure the cable connections are clean and tight and the hold down hardware is secure. Once a battery reaches its third year, have it tested annually. A car battery test identifies the deterioration level so you know when it is time to install a replacement battery. More information available in the Things to know about your car battery article. AAA members in most areas can request AAA car battery service. A professional service tech will come to your location, conduct a free diagnostic test of your car's battery and starting and charging systems, and if needed, install a new battery on the spot.
You must consider the battery type, physical size, terminal configuration, and cold cranking amps (CCA) or amp-hour (Ah) rating to ensure you get a car battery that properly fits and functions for your make and model vehicle. Installing an incorrect battery can adversely affect the car's electrical system and cause major damage if the terminal locations create a short circuit with nearby components. If you are not sure which car battery to buy, ask your auto repair professional or consult your owner's manual.
Batteries are either conventional lead-acid or the more advanced AGM design previously mentioned. Most cars on the road today use conventional batteries and some models use AGM batteries. These batteries are highly spill resistant and better able to handle repeated discharging and recharging, as occurs in cars that have engine stop-start systems to improve fuel economy. Auto manufacturers optimize car-charging systems for the battery type so AAA recommends that your replacement battery always be the same type as the original factory-installed battery.
The group number, for example Group 24, is an industry standard that defines the battery's physical size, its hold down configuration, and the type of terminals and their location. Selecting a battery with the same group number as the original equipment battery will ensure a secure fit, adequate clearance, and no cable/terminal issues. It will also allow for proper reinstallation of the important battery heat shield, if your vehicle has one. Some imported vehicles use batteries that conform to European or Asian battery standards. In many cases, a standard group number battery will fit with minor or no modifications, but pay special attention to ensure that the installation does not pose any problems. Refer to the application guide available where you purchase the battery. If you prefer, trust a AAA car battery service tech to install the correct part.
In a limited number of cars, the vehicle design makes a factory replacement battery the only possible option.
The cold cranking amps rating, for example 650 CCA, is an industry standard measure of how much electrical power a battery can provide at zero degrees Fahrenheit. Never confuse this rating with "cranking amps" (CA), a rating based on an easier test that produces inflated numbers. Some import automakers state battery power requirements using an amp-hour rating, for example 78 Ah. This rating is based on the number of minutes a battery can provide a specified level of electrical current, typically 20 amperes. To avoid electrical system problems and a visit to the repair shop, never install a battery with a CCA or Ah rating that is lower than what the vehicle manufacturer recommends. A higher-rated battery will work if it fits properly, but is usually unnecessary and may have a shorter service life in hot climates.
When your car needs a new battery, always purchase one from a high-volume seller with fresh stock. You do not want a battery that has already lost a good portion of its service life sitting on a shelf. Also, look for a battery with an extended full-replacement warranty. Quality batteries offer free replacement for three or more years if there is a problem within that period. A warranty that enters a pro-rated replacement period sooner will require a partial payment to replace the battery once the full-coverage term expires.
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