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I am curious if the following voltages I measured are bad. I looked up how to test my battery and alternator using a volt meter. I got the following three readings.
1. Car off and no electronics on: 12.61V
2. Car off and headlights turned on: 12.30V
3. Car up and running with lights on: 14.74V

I think the second reading is telling my my battery is only charging up about halfway. And the third reading is telling my my alternator is fine. Which would mean it is time for a new battery. Am I interpreting these correctly?
 

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It is the original battery, so over four years old now. So if a shop does a load test (my voltmeter is a $25 digital that does not have the ability), that would show if the battery is near the end more definitively. At a minimum I guess I should clean the terminals up, lot of corrosion. Will be interesting to see what happens when the various computerized control unit(s) reset to default.
 

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my voltmeter is a $25 digital that does not have the ability
Yes and no.

A load tester will place a load on your battery and display the voltage. If the voltage drops below 9.6V the battery should be replaced. A simple internet search will return lots of load testing videos and load testers are probably cheaper than a dealer visit.

To use your voltmeter you can get a helper to start your car while you measure the voltage. It will get you close, but the easiest most accurate method is the load tester.
 

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Fwiw, 100 amp batt. load testers, which also check the charging (alt.) and starting (starter) systems, available in analog and digital, for cheap at Harbor Freight Tools. They also offer a nice 500 amp carbon pile tester. I have both, lol.
 

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Discussion Starter #7
Yes and no.

A load tester will place a load on your battery and display the voltage. If the voltage drops below 9.6V the battery should be replaced. A simple internet search will return lots of load testing videos and load testers are probably cheaper than a dealer visit.

To use your voltmeter you can get a helper to start your car while you measure the voltage. It will get you close, but the easiest most accurate method is the load tester.
I watched the videos that have a min/max voltmeter. I will try your "duct-tape and baling wire" option where I keep a close watch on the meter when someone else starts the car to get a glimpse of how low the voltage drops (over/under 9.6V).

Thanks everyone for the feedback.
 
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I watched the videos that have a min/max voltmeter. I will try your "duct-tape and baling wire" option where I keep a close watch on the meter when someone else starts the car to get a glimpse of how low the voltage drops (over/under 9.6V).

Thanks everyone for the feedback.
The one issue with this which comes to mind is that very often, digital meters take a while to converge on the right value, meanwhile the voltage is varying with time, making it even more difficult for the meter. An old fashioned analog meter will help, but they can be kind of slow, too.

Walmart and most parts stores have load testers which can more accurately load test the battery, for free, assuming you can get it there without great difficulty. As stated earlier, the battery should be charged for this test.

Doug

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