Automotive?

Can you test the voltage of your battery with the motor off? Also, how do you know if your alternator or your battery is having issues?

8 Answers

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  • 4 weeks ago
  • don r
    Lv 7
    4 weeks ago

    You can check battery voltage with the engine off. You can check the alternator with the engine running.

  • 1 month ago

    Yes you should test the battery with the engine off. It should measure 12 volts or higher. Then in order to test the alternator, you test the battery again with the engine running. The voltage with the engine running should read around 14 volts or higher. If it does not read that high with the engine running, then your alternator is not putting out enough voltage to charge the battery.

    engine off 12 volts; engine running 14 volts

  • 1 month ago

    Easiest way to know what's going on is to go to an Auto Parts Store. They test the battery and alternator for free.

    It doesn't make any difference testing the battery with the motor shut off. You need the motor running when testing the voltage at the battery posts to find out if the alternator is charging the battery. You need a minimum of 13.7 volts or the alternator is bad.

    Source(s): Mitsubishi Master Tech
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  • 1 month ago

    Start engine, get volt meter at harbor freight, read 13.8v or higheror altrrnator is going out...

  • 1 month ago

    Using a digital volt meter: With the engine off the battery should read 12.6 volts fully charged. 12.4 volts 75% charged, 12.2 volts 50% charged, & 12.0 volts 25% charged. With the engine running you should read 13.5 to 15 volts. Any less and the alternate is defective.

  • 1 month ago

    The battery voltage should be about 12.5VDC with the engine off. When running, the battery should read over 13 but less than 15. NEVER disconnect a battery cable when the engine is running. That can blow alternator diodes. This was the standard test back in the generator days but no more. Your alternator replenishes the battery after the starter borrows power/energy from the battery to spin the engine for starting. Once the engine is running, the alternator provides nearly all power except at idle. Topping up the battery happens quickly. After only a few minutes, the alternator finishes charging the battery and continues supplying power for ignition, lights, horn, accessories. After dark, start the engine and turn the headlights on. A healthy alternator will brighten the headlights when you rev the engine (raises battery voltage).

  • 1 month ago

    Use a volt meter - black to negative, red to positive terminal. Check with engine off, read the voltage, that is the battery level. . Start car, check with voltmeter should read charge voltage.. .if it is still reading battery voltage the alternator is not working! Beyond that you need a load tester.

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