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Weird 12V Battery Issue - 5V in engine bay terminal - 12.5V at battery.

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by kgorczyn, Sep 30, 2015.

  1. kgorczyn

    kgorczyn Junior Member

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    Hi everyone, first time poster here.

    So I got into my 2011 Prius III this morning and it would not start. It opened fine via the Smartkey, dome lights lit up, hit the Start Button and everything turned off. No power whatsoever. Jumped it using one of those portable battery packs and it started right up.

    Off I went to work, about a 40 minute drive. Parked the car and turn it off, lost all power. Could not even lock my doors. Of course couldn't start it back up, had to jump it again after work. Drove it home, same thing, no power as soon as I turned it off.

    Tested voltage at the engine bay positive terminal, was getting less than 5V. OK, sounds like bad battery. This is where it gets interesting. Went to Advance Auto to get new Optima battery, installed, she fires right up no problems. 12.5V at the battery and at the Positive terminal in the engine bay.

    Bring old battery to return to the store so I can get my core money back, I asked the associate to test the battery just for fun. Battery tests a perfect 12.5 / 12.6 volts.

    Any idea what happened? I plan on putting the old battery back in my car this weekend to see if it still reads 5V in the engine bay. Associate thinks its a bad ground somewhere in the car, but why would the new battery work fine? Connections seemed OK when I took the old battery out.
     
    #1 kgorczyn, Sep 30, 2015
  2. AzWxGuy

    AzWxGuy Weather Guy

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    Perhaps a bad connection at either the positive or negative terminal connection to the 12V battery. Swapping out the battery temporarily cleaned the connection. You said the battery connections looked OK though, so it could be internal damage to your old battery that intermittently causes an internal short. Also check for corrosion where the negative terminal wire bolts to the body. Remove the negative terminal from the battery and loosen up the bolt a bit. Twist the lug back and forth to clear any corrosion and tighten it back up. Lastly, maybe the positive cable run from the battery to the engine room is shorting somewhere. Rodent damage? Collision damage? All I can think of. And welcome to Prius Chat !
     
    #2 AzWxGuy, Sep 30, 2015
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  3. bisco

    bisco cookie crumbler

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    welcome! keep an eye on the optima as well, 12.5 is low for a new battery. if ti doesn't come up to 13+, you may want to trickle it. all the best!(y)
     
    #3 bisco, Sep 30, 2015
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  4. epoch_time

    epoch_time Active Member

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    I had the same problem.. It was internal open connection( intermittant showed 12 volts before trying to ready, load would open internal batt connection) inside 12 volt battery.
    The associate didn't put a load on battery just a volt meter like you had done before.. don't even wast your time putting it back in prius.
    Just take it to another store for someone else to test it under load... if load test is done you will ask them how many amps it put out ..

    I bought exact replacement form OReilly auto for 180.00 plus core charge.. It has a 4 year waranty..
     
    #4 epoch_time, Oct 1, 2015
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  5. kgorczyn

    kgorczyn Junior Member

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    Thanks for the reply guys!

    I tested the old battery this morning again, down to 10V - Whew - Makes me feel better now that I'm pretty confident it was the battery and not the car. Car started up perfectly this morning with the new battery. Voltage was 12.65 at the terminal in the engine bay after sitting all night. Will check it again after I get home from work to see if it charged up a little bit more.

    Thanks again everyone, loving this site!
     
    #5 kgorczyn, Oct 1, 2015
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  6. dorunron

    dorunron Senior Member

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    If you are interested in making your new battery last longer than the first one, think about investing in a "smart charger". Get one that can be set for AGM. You can connect the charger to the jump post under the hood for a temporary connection. If you will keep your new battery "fully" charged it should last longer than just trusting the Prius to charge it for you.

    Best of luck to you and "Welcome to Prius Chat". (y)
     
    #6 dorunron, Oct 1, 2015
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  7. Siward

    Siward Active Member

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    I just bought 124R battery yesterday at Costco (which is not for the Prius). I brought along my multimeter and tested several of batteries on the store shelf. The were all dated 9/15 and they all tested about 12.53V DC. These Kirkland batteries are 700CCA. The 5-year old battery I replaced was 12.3V.

    I am not sure if voltage is a very accurate test of battery life. The best test is under load such as when your car is powering on.
     
    #7 Siward, Oct 2, 2015
  8. bisco

    bisco cookie crumbler

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    it's not a test of battery life, but the prius is a better maintainer than charger. when you replace the battery, it's best to start with a fully charged one. it's easy for a 12.5 volt battery to slip down a notch or two, and cause trouble with the computers, but it depends on your driving habits. ymmv.

    disclaimer: i know nothing about electricity.
     
    #8 bisco, Oct 2, 2015
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  9. Mendel Leisk

    Mendel Leisk Senior Member

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    Yup, with any new battery before installing I hook it up to my smart charger and let it run to completion.

    (bisco's disclaimer applies to me too)
     
    #9 Mendel Leisk, Oct 3, 2015
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