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Symptoms of dead 12V but charger says battery full?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by berderder, Sep 22, 2021.

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  1. berderder

    berderder Junior Member

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    Hi everyone,

    I've been having what appear to be dead 12v battery symptoms in my Gen 3 (2014). Dim interior lights, trunk locked and can't be opened unless manually, of course car not starting. I took the battery out and hooked it up to a cheap charger from Walmart. The charger reads that the battery is fully charged. Am I missing something?

    Other symptoms: cannot lock any doors, that big orange triangle indicator on the dash

    Thank you for any tips you can give
     
    #1 berderder, Sep 22, 2021
  2. jzchen

    jzchen Newbie!

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    The phenomenon is called "surface charge". After driving around some or charging with the charger, (turn off the vehicle or disconnect the charger), turn on your high beams for 30 seconds. Afterwards measure the voltage at the battery terminals and report.
     
    #2 jzchen, Sep 22, 2021
  3. Grit

    Grit Senior Member

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    Load test it.
     
    #3 Grit, Sep 22, 2021
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  4. berderder

    berderder Junior Member

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    Oh, I cannot even start the Prius
     
    #4 berderder, Sep 22, 2021
  5. Grit

    Grit Senior Member

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    Auto parts stores does test loads for free, your car can’t do test loads. Some will even charge battery for free.
     
    #5 Grit, Sep 23, 2021
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  6. berderder

    berderder Junior Member

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    Thankfully there is a little garage in walking distance I can take the battery to. Might have to do that first thing in the morning so I can make my day appointments. Not sure if leaving my battery plugged in while the charger says it's full is a good idea
     
    #6 berderder, Sep 23, 2021
  7. xliderider

    xliderider Senior Member

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    If your 2014 has its original 12v auxiliary battery, then it's time to replace it anyway. It's 7 yrs old, that's a good run for an oem battery.

    Posted via the PriusChat mobile app.
     
    #7 xliderider, Sep 23, 2021
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  8. berderder

    berderder Junior Member

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    Yeah that's true. I'm the 2nd owner and double checked my service history in CarFax - doesn't look like battery was ever replaced. I guess the other thing is it seems like it happened out of nowhere, car is in regular use and didn't give me any sign that the battery might be failing. I suppose that might just be how it is, I'm not super versed in this
     
    #8 berderder, Sep 23, 2021
  9. berderder

    berderder Junior Member

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    Any battery replacement recommendations?
     
    #9 berderder, Sep 23, 2021
  10. rjparker

    rjparker Tu Humilde Sirviente

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    Any recent charger should regulate enough to leave it on overnight. What model is the charger?

    Generally you need a charge on the battery to load test it. Unless it is absolutely dead and won't take a charge. Its doubtful a garage will have a Prius battery so they would have it delivered. There won't be many options, maybe one brand at an auto supply or the Toyota OEM (best if in stock) at the dealer.
     
    #10 rjparker, Sep 23, 2021
    Last edited: Sep 23, 2021
  11. berderder

    berderder Junior Member

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    This is the charger I have:

    Everstart Maxx 3 Amp 6V/12V Automotive Battery Charger (BC3E) - Walmart.com
     
    #11 berderder, Sep 23, 2021
  12. rjparker

    rjparker Tu Humilde Sirviente

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    I would put that charger on overnight. Be sure its set for 12v. Its possible the car might go to Ready in the morning if there is any hope for the battery.
     
    #12 rjparker, Sep 23, 2021
  13. berderder

    berderder Junior Member

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    I’ll give it a shot, thanks. I’m just confused why the charger says the battery is already full and am afraid of overcharging it
     
    #13 berderder, Sep 23, 2021
  14. xliderider

    xliderider Senior Member

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    FYI, our oem battery didn't give any signs of failing either, until we couldn't unlock the door using the sks, or keyfob,and the car wouldn't start or go into Ready.

    Posted via the PriusChat mobile app.
     
    #14 xliderider, Sep 23, 2021
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  15. rjparker

    rjparker Tu Humilde Sirviente

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    In the morning, be sure to try three times if it does not go to Ready. Power off between tries. Often necessary after a total discharge. Even if it runs, go directly to an auto supply and have it checked.
     
    #15 rjparker, Sep 23, 2021
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  16. berderder

    berderder Junior Member

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    Yep, exactly what happened to me. I guess that's just how it can happen
     
    #16 berderder, Sep 23, 2021
  17. jerrymildred

    jerrymildred Senior Member

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    Did you check the connection of the ground wire from the battery to the car body? It doesn't matter how good the battery is if that's loose or corroded.
     
    #17 jerrymildred, Sep 23, 2021
  18. berderder

    berderder Junior Member

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    After I went back into the trunk I noticed about a half inch of oily liquid at the bottom of the battery compartment. Yeesh. I used gloves and cleaned it up with rags - the liquid didn't smell like anything, just water. Probably shouldn't have smelled it lol.

    But yes, otherwise the contacts looked pretty good. Clean and the battery itself was dry, unlike the floor of the compartment. After about 4 hours of the battery being hooked up to my charger in the basement, the car still didn't start after reinstalling. I am now looking at possibly picking up a new TrueStart battery to replace it.

    I spent the majority of winter in very very cold Vermont, I think that probably knocked some time off its lifespan
     
    #18 berderder, Sep 23, 2021
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  19. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    yeah I doubt your charger is a capable tester. Don’t conflate the charger being “done”, with the battery being “good”.

    if you want to DIY the load tester, look into Solar BA9 for one.
     
    #19 Mendel Leisk, Sep 23, 2021
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  20. jerrymildred

    jerrymildred Senior Member

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    I just put a new Truestart in my wife's 2017 a couple days ago. Since the Gen 4 battery is lead acid (wet) it probably cost less than the AGM you'll need to get. Mine was only $180 minus a $10 coupon.
     
    #20 jerrymildred, Sep 23, 2021
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