New OEM 12V shows 11.5V after two months?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by ericspoor, Mar 7, 2019.

  1. ericspoor

    ericspoor Member

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    Question for you all- Car wouldn't start this morning, and the 12V measured 11.5V. This battery is only a few months old, though over the past 4 days my prius has been giving me the "parking brake actuator not engaged" alert on every other startup + yesterday the driverside window wouldn't auto-rolldown. Any idea why the 12V would be so weak so soon? And, if i jumpstart the battery, drive the prius and charge up the 12V would that fix the problem or is that a band aid? Thanks for any help
     
  2. Mendel Leisk

    Mendel Leisk Underfoot

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    Might have been a dud from the outset. Did you check the voltage when you got it? Did the seller demonstrate it's health with an electronic load tester, or was it mail order?

    Might be connections. Did you check the voltage directly at the battery posts?

    Is the car driven more-or-less daily, or does it frequently sit for multiple days, and then just short trips?

    Any add-on stuff that could be draining: dash cam that stays on when the car's off, alarm system, for example?
     
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  3. JC91006

    JC91006 Senior Member

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    I would fully charge the battery and see how it performs.

    How are you getting the voltage readings?
     
  4. ericspoor

    ericspoor Member

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    I did check voltage at the battery posts, the car is driven daily, and no add-on electronics.

    so flashback to a few months ago: I had a mobile mechanic drive to toyota to pick up the 12v then drive to my parking lot to install it. After he installed it, the car started up, I let it idle for 30 seconds then i shut the car off to go grab my work items. When I returned to the car, it wouldn't start. The mobile mechanic jumped it and I drove it to work, worked all day, then drove it home no problems. the day after that, it wouldn't start again. At that time I noticed the ground was loose so I tightened it, and measured the 12V at 12.4, and the car started.
     
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  5. ericspoor

    ericspoor Member

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    I used a multimeter with the prongs touching the battery posts
     
  6. sam spade 2

    sam spade 2 Senior Member

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    It is possible that the battery has never been fully charged since installed.
    You should do that NOW with a manual charger.
    Many cars these days won't fully charge a completely dead battery.......and many new ones come dead from the factory.

    You should also test the voltage when the car is in "drive" mode; should be around 14.2.

    I hope you have some paperwork that shows you bought the battery at a dealership.
    I would be tempted to take it there to have the battery tested......AFTER it is fully charged.
     
  7. ericspoor

    ericspoor Member

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    I ordered a supercapacitor jump starter to charge up the battery. itll arrive this evening. at that point ill fully charge it and see the results
     
  8. Mendel Leisk

    Mendel Leisk Underfoot

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    A jump pack is a bandage, don't think it'll remedy the battery?

    Try something like a CTEK 4.3 for charging.

    I'm at the point now, I will not accept a new battery without first testing with an electronic load tester. They hook up directly to the post, you input the battery type, the rated Cold Cranking Amps, and it tests and reports, voltage and measured CCA, plus gives a verdict: good, good-but-recharge, or fail. Solar BA5 is on example, a DIY level tester.
     
  9. Skibob

    Skibob Senior Member

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    Sounds like your mobile mechanic was not very good if he left the ground loose. Have you checked the ground cable to body bolt? The positive terminal to Fusible nut? Are they tight?
     
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  10. ericspoor

    ericspoor Member

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    well i took the supercapacitor jump starter and hooked it up to the 12v. it was able to charge it up to the point where I could start the prius. Drove it for 20 mins on the highway immediately after, pulled back into my parking spot and measured the voltage while it was in ready position: 12.29V. We'll see what it does tomorrow morning!
     
  11. JC91006

    JC91006 Senior Member

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    If you measure 12.29v in READY mode, then your car is not charging the battery. The car should read 13.8v or above in READY mode
     
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  12. ericspoor

    ericspoor Member

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    i may have misspoke- i drove into my parking spot, put it in park/set the e-brake, didn't turn it off and walked to the trunk and measured the voltage- i assume that meant i was in ready mode?

    If so, any ideas as to why the car wouldn't be charging the battery?
     
  13. JC91006

    JC91006 Senior Member

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    Your dc-dc converter is not working. The alternator of the prius
     
  14. ericspoor

    ericspoor Member

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    hm thats not good news. would the <13.8 reading also occur if the 12v battery was a "dud"?
     
  15. ericspoor

    ericspoor Member

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    and a follow up question- lets assume the dc/dc converter is bad. how long if at all can i drive the car with that issue? Would it necessitate jumping the car each time?

    given that the car originally read 11.5, then after driving it read 12.29, would that not be evidence of charging occuring, or is that charging all related to the jumpstarter?
     
  16. JC91006

    JC91006 Senior Member

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    You would not be able to drive far if the 12v battery is not charging. You may get stranded.

    You mentioned you charged the battery a bit so it can start. You can check the voltage tomorrow morning, I suspect it would be low again
     
  17. ericspoor

    ericspoor Member

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    You are correct it was low, thought this time at 12.02 instead of 11.5v. Pardon my ignorance-wouldnt this indicate a bad 12v that cant hold w charge rather than a bad inverter that cant charge a good battery?
     
  18. ericspoor

    ericspoor Member

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    Update: drove the prius to work. Once i larked the 12v measured 12.4v with the car off- would this indicates the car is charging the battery? (Since pre trip it measured 12.02?)
     
  19. sam spade 2

    sam spade 2 Senior Member

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    That is NOT a good way to charge a battery.......and it really isn't intended to do that.

    AND......you aren't listening close enough.
    IF the car is in "ready" mode, that is ready to drive, the voltage at the battery needs to be at least 13,8 volts. If not, one of two things is happening: As mentioned before, your changing system is shot (most likely) OR there is a huge short somewhere drawing down the voltage.

    Either way, this is likely NOT something you can, or should be trying to fix yourself.
    Time for a shop visit.
     
    #19 sam spade 2, Mar 8, 2019
    Last edited: Mar 8, 2019
  20. ericspoor

    ericspoor Member

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    sorry let me clarify- I used the jumpstarter to jumpstart the car, i didn't leave it attached to the battery to charge it after the car started.

    edit: also since its a supercapacitor its not really able to charge the battery, it just takes in some of the 12V's juice, then releases it at once to start the car i think
     
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