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What does this say about my 12v battery?

Discussion in 'Gen 2 Prius Main Forum' started by davethomasowns, May 13, 2013.

  1. davethomasowns

    davethomasowns New Member

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    Hello,

    My 2009 Prius would not start yesterday so I had to have someone jump me to get home. Now I am wondering if I need to replace my 12v battery or if it was just drained. I found online how to access the system check menu and these are the readings:

    Push power once (no brake)- 11.6v with headlights on
    Pushed power again (no brake)- went down to 9.5v with headlights on
    Engine on- Stayed at 14.0v

    Will driving the vehicle awhile charge it up more? Or is the battery weak and I need to replace it? Thanks so much in advance!

    [​IMG]
     
    #1 davethomasowns, May 13, 2013
  2. dorunron

    dorunron Senior Member

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    I would suggest you install a new 12 volt battery. It is a DIY job. I changed our's earlier this year. It is a straight forward job if you are mechanically inclined.

    FWIW, a fully charged 12 volt normally reads running the test you did like the following.

    Aux Mode (Step 1 of Test) 12.6 or higher
    Ign On Mode (Step 2 of Test) 12.4
    Ready Mode: (Last Step) 13.8 to 14.2

    The last step only shows that the charging system is working. What is important is the first two steps. 9 something is VERY low for the second part of the step.

    Best of luck to you.

    Ron
     
    #2 dorunron, May 13, 2013
  3. kenoarto

    kenoarto Senior Member

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    Prius battery takes a loooooong time to fully charge. How long did you charge it?
     
    #3 kenoarto, May 13, 2013
  4. dorunron

    dorunron Senior Member

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    FWIW, if you own a battery charger hook it up. Set it on AGM 4 Amp and let it fully recharge the battery. Then let the Prius set over night and run the test again. If the battery will hold a charge keep driving it. If it drops quickly, well then it would be time to think about a replacement.

    I charged ours all last summer and made it through the winter until the first of the year. It finally gave up the ghost and had to change ours. The voltages were a lot higher than yours though. I didn't wait until I had to jump the car.

    Good luck to you.

    Ron
     
    #4 dorunron, May 14, 2013
  5. Addictive Sundew

    Addictive Sundew New Member

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    Ready mode is related to "Hybrid battery"??

    While: Aux Mode, and IGN On mode is related to the smaller 12V battery?
     
    #5 Addictive Sundew, May 14, 2013
  6. Addictive Sundew

    Addictive Sundew New Member

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    ** subscribed
     
    #6 Addictive Sundew, May 14, 2013
  7. dorunron

    dorunron Senior Member

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    Actually Ready Mode in the test which is being referred to shows that the DC to DC converter is working properly and charging the 12 volt auxiliary battery.

    You have to remember that the 12 volt auxiliary batteries purpose is strictly to power up the computers and relays to allow the Prius to go into Ready Mode. Once in Ready Mode then the power comes from the traction battery which is charged as needed by either regeneration from the brakes and/or the ICE. The only other time the 12 volt battery comes into play is if you are in auxiliary mode listening to the radio or using an alternative electric load. But to answer your question, the ready mode section of the test is more about the DC to DC converter (charging system) than anything else.

    I hope this help you. Other's here can probably explain it better and in more detail than myself.

    Good luck to you and "WELCOME" to Prius Chat.

    Ron
     
    #7 dorunron, May 14, 2013
  8. blueumbrella

    blueumbrella Member of Prius Regeneration

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    I am considering replacing my 12v battery this fall, preemptively. I know getting 5 years out of a battery (IMO) is pretty good.
     
    #8 blueumbrella, May 24, 2013
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