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Does My 12 volt battery appear bad?

Discussion in 'Gen 4 Prius Care, Maintenance and Troubleshooting' started by Darklandscape, Jul 14, 2024 at 8:45 AM.

  1. Darklandscape

    Darklandscape Junior Member

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    I put the car in ready mode and turned just the headlights on. For 20 minutes the 12 volt showed between 13.59-13.85 volts, is it supposed to charge for this long?

    I turned the car off with the headlights on, the car went from 12.56 to 12.21 in 3 minutes.
    Is this a normal level of discharge?

    Battery is 4 years old
     
    #1 Darklandscape, Jul 14, 2024 at 8:45 AM
  2. Doug McC

    Doug McC Senior Member

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    Your battery is fine. Your method of testing it may not be the best, but it’s fine. As long as there’s a load on it in READY the system will charge at a rate that’s required to compensate for the load.
     
    #2 Doug McC, Jul 14, 2024 at 9:50 AM
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  3. Mendel Leisk

    Mendel Leisk Senior Member

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    Look into the new generation of electronic load testers. You use them with car off. If I was shopping for one it’d likely be Solar BA9 (I’m familiar with it predecessor, BA5, which I currently have and use), but there are lots of choices.
     
    #3 Mendel Leisk, Jul 14, 2024 at 11:12 AM
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  4. BiomedO1

    BiomedO1 Senior Member

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    That's fine, though an informal test. It would be worrisome if the voltage dropped below 11.75 under the same conditions. I believe you'll start encountering sensor error messages down around 10.5 or less.

    Hope this helps...
     
    #4 BiomedO1, Jul 14, 2024 at 11:31 AM
  5. bisco

    bisco cookie crumbler

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    get a free load test at many auto parts stores
     
    #5 bisco, Jul 14, 2024 at 8:11 PM
  6. FuelMiser

    FuelMiser Senior Member

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    or buy your own TOPDON BT100 battery tester
     
    #6 FuelMiser, Jul 15, 2024 at 5:37 AM
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  7. vvillovv

    vvillovv Senior Member

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    Geb 3 s have a diagnostic mode you get to on the MFD. Look in your owners manual under the MFD stuff.
    It shows amongst other stuff the 12 volt static reading.
    I've never tried this, but it might be possible to see in all three of Prius On states. Acc, On and Ready.
     
    #7 vvillovv, Jul 15, 2024 at 10:22 AM
  8. ColoradoBoo

    ColoradoBoo Senior Member

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    THIS! I love my battery tester and use it all the time.
     
    #8 ColoradoBoo, Jul 15, 2024 at 10:29 AM
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  9. BiomedO1

    BiomedO1 Senior Member

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    Call me old school but I still like the standard carbon pile load testers. It doubles as a hand warmer in the winter.:p:D:ROFLMAO:
     
    #9 BiomedO1, Jul 15, 2024 at 7:57 PM
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