The typical lead-acid car battery will last about four years. The good news is that car batteries are fairly inexpensive to replace. The bad news is it's hard to tell when your car battery is on the way out. Even battery tests can't give you a definitive reading on the state of your battery. The test can only present an assessment of the state of your battery when it's tested, without the context of the battery's chemical composition before or after. So when your car battery dies, it just dies, often with what seems like no warning - - and inevitably at the worst possible time.
There are things you can do to help prolong its life. Consistently exposing a car battery to high temperatures can affect the chemical reaction that occurs within it, hastening its demise. Two more ways a battery can prematurely degrade are charging it inconsistently though infrequent driving and not letting it go through a full charging cycle. The short charges, without a full cycle, occur mostly when you take a lot of short drives -- the battery never gets a chance to charge fully. Another way to sap a car battery's life is to attach a lot of other devices to it, such as an MP3 player, cell phone or GPS receiver, all of which create extra draw on battery power. And if your car battery sits loosely within your car and gets banged around, its physical integrity can be adversely affected.
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