How do you know if you need a new battery?

It's a dumb question, I guess, but are there "symptoms" to watch or listen for? Is it simply a matter of the battery's age?
How do you know when it's time to replace the battery?

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After 4 or 5 years it's time to have the old bat. "load tested" and then you'll often buy a new one to avoid breakdown.
Of course one can be "economical" and wait for the old bat. to be dead one day - and so be sure, absolutely, that the very last mile or day was wrung out of the old bat.
It, like most car maintenance, is a trade off time (yours) vs. $$ (also yours). A $100 bat. over 5 years is $20/ yr or $.385/week. Not much saved by waiting.
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You could measure it's voltage while drawing lots of current (load testing) but just cranking the motor is pretty good load testing ..... therefore, if it won't crank much (usually happens in winter when chemical reactions slow down anyway) or will barely crank WITH the lights on --> time for a new one
cheers, guenter

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Load testing is one way... electrolyte is another way. Autozone battery is the best bang per buck... They will test your battery there too.
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As far as symptoms, many batteries will give some sign of difficulty turning the car over, especially on a cold day. But some will go with little or no warning. If it's over 6 years old, I'd just replace it, as they don't last forever and considering the cost of a battery, vs the cost of getting stuck somewhere, it's a good idea.
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