Do I need a new alternator or battery?

Written by jay motes
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Do I need a new alternator or battery?
Determining if the battery or alternator needs replaced can be difficult. (dead battery image by Katrina Miller from

Both a bad battery and a bad alternator can cause a vehicle's electronic system to fail, resulting a car that will not run or start. Diagnosing the correct problem can help a car owner save money by buying the proper part.

Battery and Alternator Symptoms

Symptoms of a failing battery and alternator can be similar. In general, battery problems are usually spotted when starting a car. Cars that are operating normally but are difficult to start may have a bad battery. Dim or fluctuating headlights while driving are typically a sign of a failing alternator.


Car owners can test the electrical output of the system using a voltmeter. In addition, most auto parts stores will test both batteries and alternators for free. Parts stores can typically test alternators and batteries that have been removed from the car as well as those still mounted in the car.

Other Problems

Electrical systems can fail for a number of reasons other than a bad battery or alternator. Corroded battery cables or loose wiring to the alternator can also cause problems. A loose belt may slip and cause the alternator to fail to charge. Car owners should check these simple and inexpensive-to-fix problems before purchasing a battery or alternator.

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