How Do I Know If It Is My Car Battery or My Alternator?

by Robert Russell
itstillruns article image
Thinkstock/Comstock/Getty Images

The battery and alternator work together to keep your car running. The battery stores electricity for the car and the alternator recharges the battery. The battery supplies the car with power when the car is not running. That is why you can sit and listen to the radio with the engine turned off. Once the engine is turned on, the alternator continuously recharges the battery. If the alternator is not working properly, the battery will quickly run out of power. Alternators and batteries are expensive, so before you start switching out parts you need to figure out which component is causing a problem.


Step 1

Check the condition of the battery. A lack of maintenance can lead to battery problems. The cables should be tight. Clean any corrosion off the connectors. If the battery is drained or its power is low, check to see whether you left the headlights or an interior light on. If the battery is constantly dying, this is a sign of a bad alternator.

Step 2

Make sure that the alternator belt is tight. If it is loose, the alternator will not function properly.

Step 3

Check to see if the engine will turn over. If the engine does not turn over you probably have an alternator problem.

Step 4

Jump start the car with jumper cables. Check the battery with a voltage meter. Connect the negative terminal to the negative test lead and the positive terminal to the positive test lead. Select the correct range on your voltmeter that corresponds to the voltage of the battery. Alternators should put out between 13.5 and 14.5 volts. If the battery is below 13 volts, the alternator is probably bad.

Step 5

Drive to an auto parts or auto repair shop test the alternator. Some shops will do this free of charge. If the alternator is bad, the car will run off the battery for only about 30 minutes, so have a friend with jumper cables follow you.

More Articles

article divider