Immediate 12V replacement?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by abdullah arslan, Dec 1, 2020.

  1. abdullah arslan

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    just measured the voltage for the first time since bought my 2010 prius V approximately 20 months ago. It showed 10.5-10.6 before driving it. The outside temp was 36 degrees. I dont know the last time replacement so do I need to install a new one right away? So far, it has always started without problem. Acc to table below, it seems almost empty. Also I can say that the mpg is kinda dropped about 3-4mpg comparing to last year
    And one more thing, is it better to go with standard Toyota battery? For my other car, I used Interstate and liked so much
    Thanks
    20201201_145220.jpeg tapatalk_1606851001258.jpeg

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  2. Mendel Leisk

    Mendel Leisk Sand Pounder

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    Measure with the car off with a digital voltmeter.

    Better: have it tested with electronic load tester.
     
    #2 Mendel Leisk, Dec 1, 2020
    Last edited: Dec 1, 2020
  3. Grit

    Grit Senior Member

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    According to the “voltage to state of charge” table, your battery is 10.5 volts so it’s 0% charge, your battery is completely dead. how come you were able to get into diagnostic mode then?!
     
  4. abdullah arslan

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    I guess it's inaccurate. Just measured 12.5V with multimeter, after 2 hours I got to home. Assuming nothing to worry about
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  5. Mendel Leisk

    Mendel Leisk Sand Pounder

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    Check it once more, first thing in morning, just in case it's reading a little high, due to "surface charge". The car is charging as you drive, and freshly charged will read a little high. Pop the hood the night before if practical, so you don't "wake up" the car at all, before taking reading reading.

    If it's still reading around 12.5 you're ok for a while. 12.3~12.4, it's starting to slip slide.
     
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  6. rjparker

    rjparker Senior Member

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    The best approach is to change it if its original. Plus compare the mfd display to your measured voltage. My bet is they will be very close, within a couple tenths of a volt.

    Driving it will charge it using 13.5v - 14.8v. The real question is: What does it read after sitting for ten or more hours? Modern cars draw current continuously even when off but a good battery should retain adequate voltage for at least three weeks. 10.5v is poor. My battery usually reads 12.3v or better after sitting overnight.

    It is possible the rear hatch was not closed all the way or a map light was left on causing a temporary excessive discharge.

    While likely not a factor, some voltmeters like the "free" harbor freight units often read high.
     
    #6 rjparker, Dec 1, 2020
    Last edited: Dec 1, 2020
  7. abdullah arslan

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    Sure I ll check both out tomorrow morning and will let you guys know, first with multimeter, and then from dash. Btw, I keep measuring with multimeter until the numbers doesn't change, that's my voltage reading
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  8. edthefox5

    edthefox5 Senior Member

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    So rare the poster has a meter thats great.

    Try this:

    With car off measure the battery. Write that down.

    Then with car still off turn on the headlights in high beam for exactly 5 minutes. After 5 turn them off and wait one minute and then measure the 12 volt battery again.

    Its a pretty benign load test and the battery should not have dropped one volt. What's yours measure?
     
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  9. jzchen

    jzchen Senior Member

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    30 secs on high beams is enough says Toyota. Come back with result...

    moto g(7) power ?
     
  10. edthefox5

    edthefox5 Senior Member

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    Show me where Toyota says that.

    My 3 year old Optima yellowtop has no problem with this test it does not lose a volt.
     
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  11. abdullah arslan

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    Good morning gentlemen, I did the tests per your instructions, three measurements:
    1) After overnight, 12.38-12.40V
    2) After 5min headlights on and 1min off, 12.20V
    3) Prior to starting car, from dash 10.4-10.5V
    Btw, the outside temp was 27-28
    I guess the car passed the test
    Thanks again
    20201202_090444.jpeg

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  12. Mendel Leisk

    Mendel Leisk Sand Pounder

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    Those first measurements are ok but lowish. If you measured Cold Cranking Amps (with electronic load tester) i suspect you'd get a value either at spec (around 325?) or a little below.

    I'd take that as a impetus to start battery researching, get a new one sooner than later.
     
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  13. sam spade 2

    sam spade 2 Senior Member

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    That may NOT be a good assumption. It is better to test after it sits for ~12 hours of non-use.
    An AGM battery that is healthy and fully charged should measure about 12.8. Tenths of a volt are important.

    It sounds to me like you are getting close to needing a new one.
     
  14. sam spade 2

    sam spade 2 Senior Member

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    12.4 with no load shows that it is mostly worn out.
    It might last a year more......or it might only last a few weeks.

    If it is over 7 years old, you NEED a new one.
    Unless maybe if you like unexpected adventures.
     
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  15. abdullah arslan

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    I see your point, I had no knowledge about AGM batteries. It's time to research as Mendel said, and get a new one soon. Probably these batteries cost more than traditional ones. I ll check out the Dealer for OEM one and also just saw the DieHard is $209 after core refund.
    Btw, the car is at 249k mileage right now, looking forward to posting the photo of 250.000 :D
     
  16. Grit

    Grit Senior Member

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    So according to your table, your battery is 0% charge. Passing score :whistle:
     
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  17. rjparker

    rjparker Senior Member

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    The thing that bothers me is the dash voltage being ~2 volts off the measured. Did you measure at the jump point in the engine fuse box? That is the place where all the systems get their power. In my experience the dash/mfd voltage readout is accurate. This morning I ran the headlight test to compare my dash to the fuse box jump point. They were within 0.020 vdc of each other. Even less when in Ready.

    The first thing that comes to mind is the accuracy of your voltmeter. If you measured at the battery, I would be concerned about a 2 vdc voltage drop, assuming the system's voltage monitoring is as accurate as I expect it is. If you measured at the fuse box then I would be concerned about the connections to the ecu responsible for reporting the voltage. I don't think you would have a faulty ecu without codes.

    As far as the battery goes, there is often a date code on them. Plus any auto supply will load test yours for free.

    Here are my readings today. The top set is after the headlight test, the bottom is in Ready mode while charging from the system. Note the display values compared to my meter.

    CD681EB7-0320-4CAF-92EF-0F1A1CA3B563.jpeg
     
    #17 rjparker, Dec 2, 2020
    Last edited: Dec 2, 2020
  18. Mendel Leisk

    Mendel Leisk Sand Pounder

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    The car displayed voltage is maybe dropped due to loads.
     
  19. abdullah arslan

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    Agreed with you, I measured the same as you did, positive from the fuse box, plugged to the frame for negative. I think better to have it measured at an auto store.
    One last thing, should I stick to Toyota battery or DieHard/Duralast matters in terms of performance/mpg?
    Found this deal upload_2020-12-2_14-4-39.png but no core return will happen for this!
     
  20. rjparker

    rjparker Senior Member

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