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Electical shorting out? 12v Battery dies in 30min but starts up with a few tries

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by MorganArts, Dec 24, 2014.

  1. MorganArts

    MorganArts New Member

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    I'm trying to solve a mystery here... 2012 Prius with 50k miles:

    4 times this month my 12v battery has "appeared" dead. Smartkey doesn't work. Nothing lights up when I get in, and usually have to push the Power button a few times - but it will get back into Ready mode. Clock will be reset, so I can see that the batter is seeming to lose power within 30min of turning it off.

    The first time I jump started it (but the electrical started right back up the minute I connected the jumper cables to another battery, without having to turn either car on). So the second-fourth times I just remained patient and kept pushing the button.

    Tested the battery at the dealership and checked the connections. It's reading like it's brand spankin' new, so they don't want to replace it. They couldn't replicate the problem or find anything wrong.

    Update: Tonight I pulled into a parking lot. Shifted to Park, but remained in the car about 5 min (lights off, radio off, heat off) to do some cleaning. The engine started up just as I was ready to get out. So I hit the Power button and the electrical display on the dash (the one that will tell you how long your trip was, mileage etc) just shorted out - much like a computer with the plug being pulled. All lights/electrical went off. As before, it took a few tries, but eventually the Power button worked and the car was back on.

    I've searched the forums and not finding anything similar. . . Anyone?
    I have a mystery that
     
    #1 MorganArts, Dec 24, 2014
  2. edthefox5

    edthefox5 Senior Member

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    No mystery at all.

    Its beyond most of us but dealers seem unable to diagnose the 12 volt battery.

    Complaints of dead 12 volt battery on all models
    Is the most posted subject on this site.

    Its because the 12 in a Prius is half the size of a regular
    Car and will not tolerate interior lights left on all night.


    Usually if the little 12 goes dead once or twice its never
    The same. And will never hold a full charge again.And jump starting a Prius is kinda
    Dangerous.
    Buy a new battery. If your still not sure hers a simple test. At night before you start the car turn the headlights on and while watching the headlights start the car. If the headlights dim even slightly the battery should be replaced.

    The most prevalent reason the 12 goes dead
    On a Prius is the owner does not lock the car every time
    They get out especially in the garage.

    If attemprd to lock with the fob if door or hatch ajar
    It will not allow u to lock the car alerting u there's an interior light on.
     
    #2 edthefox5, Dec 24, 2014
  3. bisco

    bisco cookie crumbler

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    your last sentence is a mystery.:p
     
    #3 bisco, Dec 24, 2014
  4. GregP507

    GregP507 Senior Member

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    If the dealer tested the battery "as-new" my first response wouldn't be to replace it. My suspicion is in the electronics, based on this story. It sounds like a fault in one of the primary electrical systems, before it gets to the computer, (which probably would have generated a code). It's possible that the DC-power control circuitry is cutting out, causing you to lose all power and resetting the clock. Like most electronics, they can work intermittently for a while before they fail completely.
     
    #4 GregP507, Dec 24, 2014
  5. DoubleDAZ

    DoubleDAZ Senior Member

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    He's suggesting it can be a good idea to always lock the car, even in your garage, because then you always know you didn't accidently leave something on that might kill the battery. It's similar to those who suggest always using the parking brake to avoid the car rolling that little bit when you park.
     
    #5 DoubleDAZ, Dec 24, 2014
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  6. edthefox5

    edthefox5 Senior Member

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    Sorry.

    Yes always lock the car with the fob no matter where it is as it will not allow you to arm the car if hatch ajar.

    Most prevalent reason for a dead Prius 12 volt.
     
    #6 edthefox5, Dec 24, 2014
  7. bisco

    bisco cookie crumbler

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    no, meant the o/p, see his last sentence.
     
    #7 bisco, Dec 24, 2014
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  8. DoubleDAZ

    DoubleDAZ Senior Member

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    Ops, sorry. I see what you mean.
     
    #8 DoubleDAZ, Dec 24, 2014
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  9. Easy Rider 2

    Easy Rider 2 Senior Member

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    While I agree with the battery being the most likely culprit, it would be easy to verify that with a multimeter at the time of failure.
    It is also possible that a cable connection is not making good contact. The negative cable from battery to frame is a common source of problems.
     
    #9 Easy Rider 2, Dec 24, 2014
  10. edthefox5

    edthefox5 Senior Member

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    Oh yeah....like he got cut off maybe.
     
    #10 edthefox5, Dec 24, 2014
  11. bisco

    bisco cookie crumbler

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    wife was probably telling him to get off the 'net!
     
    #11 bisco, Dec 24, 2014
  12. MorganArts

    MorganArts New Member

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    GregP507, Thanks for offering up another idea for us to check. We asked the dealer to check the connections to rule that out, but will have them double-check when we ask for the DC-power control circuitry to be looked at.

    I'm fastidious about locking the doors, because YES I have walked out of the car with it still running (newb!) so that's my reassurance I've not left anything on. Will report back if I get new info.
     
    #12 MorganArts, Dec 29, 2014
  13. Easy Rider 2

    Easy Rider 2 Senior Member

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    You also need to keep in mind that batteries which test "good" sometimes are not.
     
    #13 Easy Rider 2, Dec 29, 2014
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