12v battery / charging questions

Discussion in 'Gen 2 Prius Main Forum' started by misterdean, Jan 12, 2024.

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  1. bisco

    bisco cookie crumbler

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    looks good. will be interesting the next few days
     
    #21 bisco, Jan 17, 2024
  2. misterdean

    misterdean Member

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    12.44 car off trunk open
    12.38 accessory mode
    12.25 ready mode
    13.97 engine running
    12.54 after after 7 hours doors locked crawled through window
     
    #22 misterdean, Jan 17, 2024
  3. misterdean

    misterdean Member

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    does that look normal? going from 12.72 to 12.44 with the car off seems like a big dip.
     
    #23 misterdean, Jan 18, 2024
  4. bisco

    bisco cookie crumbler

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    can you clarify the timeline in post 22?
     
    #24 bisco, Jan 18, 2024
  5. misterdean

    misterdean Member

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    i tested the battery in my home and it was 12.72. since i got 12.72 two days in a row i put the battery in car and did all those tests immediately after except the one where i waited 7 hours.
     
    #25 misterdean, Jan 18, 2024
  6. bisco

    bisco cookie crumbler

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    so it dropped from 12.72 to 12.44 after you hooked it up?
     
    #26 bisco, Jan 18, 2024
  7. misterdean

    misterdean Member

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    yes
     
    #27 misterdean, Jan 18, 2024
  8. bisco

    bisco cookie crumbler

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    so that's everything in the car powering up that normally stays powered up with the car off.

    that it continues to drop as more things get powered up through the mode transition, the the inverter kicks in and is charging the battery, then it settles into a resting voltage at 12.54 and there will be a continual drain with the car off.
    so you want to start with the 12.54, and check it each morning before starting the car to see how much it drains each day.
    a good battery won't fall much from the 12.54 over a week or so, but a tiny amount every 24 hours.
    and if you drive everyday, it should hold at the 12,54
     
    #28 bisco, Jan 18, 2024
  9. misterdean

    misterdean Member

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    correct. hooked up the battery and then proceeded to test in the order listed. i know there is going to be drain on the battery. i just wasn't sure if that amount that quick was concerning.
     
    #29 misterdean, Jan 18, 2024
  10. bisco

    bisco cookie crumbler

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    i can't say how much is normal. most likely, the weaker the battery, the more it drops on load.
    that's why a load test is the final word.
    but more importantly, it's how the 12.54 holds up now.
     
    #30 bisco, Jan 18, 2024
  11. misterdean

    misterdean Member

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    12.54 was crawling through the window after 7 hours. i can't do that test daily cause i don't have a garage and i can't leave my window down for a week. my daily tests have to be like the first one, car off and trunk open.
     
    #31 misterdean, Jan 18, 2024
  12. bisco

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    rereading your first post to refresh my memory, i see it's a new battery. if it's agm, it should have been at least 12.8 volts so i would say it's lost a little something already. does it have a date on it?

    and 12.54 is definitely too low for a new battery in the car. mine was still reading 12.7x in the morning after a few years. but it's garaged in a fairly mild climate. heat does a number on them.
     
    #32 bisco, Jan 18, 2024
  13. misterdean

    misterdean Member

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    it is AGM, the one that's suppose to be in it S46B24R date 10/23.

    i thought 12.7X was low after a fresh charge. i read a few threads that said a new battery should be in the 12.8-12.9 range. i also read a few threads that said batteries that were several years old sat in their car that wasn't driven at all for 3-6 months and started right up. mine is brand new and 11.8X in 2 months with light driving.
     
    #33 misterdean, Jan 18, 2024
    Last edited: Jan 18, 2024
  14. bisco

    bisco cookie crumbler

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    are you using a charger with agm capability?
     
    #34 bisco, Jan 19, 2024
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  15. misterdean

    misterdean Member

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    yes

    good thought
     
    #35 misterdean, Jan 19, 2024
  16. bisco

    bisco cookie crumbler

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    did you get readings yesterday and this morning?
     
    #36 bisco, Jan 19, 2024
  17. misterdean

    misterdean Member

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    yes sir, was waiting until i have more results.
     
    #37 misterdean, Jan 19, 2024
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  18. Mendel Leisk

    Mendel Leisk Senior Member

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    Reading voltage gives very little indication of the battery’s resilience; consider a conductance test. Watch video in post #19.
     
    #38 Mendel Leisk, Jan 19, 2024
  19. misterdean

    misterdean Member

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    i watched the video. i understand voltage is only half the story. the same can be said about the CCA. when i was messing with the previous battery, i took it to a shop, they tested the CCA and the voltage. it passed, and the shop told me the battery was good. the CCA was actually slightly above what it was rated at. it wasn't until i tested it daily and you guys saw the voltage dropping that it was determined to be bad. i will be bringing it to a shop for a load test the next time i'm using the car. i'm willing to be thorough. daily tests is part of being thorough.
     
    #39 misterdean, Jan 19, 2024
    Last edited: Jan 19, 2024
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  20. misterdean

    misterdean Member

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    nobody has said anything about it, but something that has been on my mind. my first test with the car off and the trunk open, was 12.44. but the last test, crawling through the window, came back 12.54. does this not seem strange to anybody? i know i had the engine running for the previous test, but it was only running for a full minute at the most, and 7 hours had past so surface charge was gone. is going from 12.44 to 12.54 in a minute normal? that seems like a significant bump for such a small amount of time.
     
    #40 misterdean, Jan 20, 2024
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