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I don't drive much. How can I keep my 2013 Prius c 12v battery in good shape?

Discussion in 'Prius c Care, Maintenance and Troubleshooting' started by RTW, Nov 9, 2023.

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  1. Mendel Leisk

    Mendel Leisk Senior Member

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    If you set your multimeter to ohms, clamp one lead to bare metal (the u-bolt on door opening for door latch maybe), and touch the pins with the other lead. The one that drops ohms to zero (finds a path) is negative; the other is 12 volt positive.

    Conversely you can test which pin is 12 volt positive with a gizmo like the attached: clamp it’s lead to bare metal, then touch the connector pins with the probe; touching the positive pin will cause the light (in it’s handle) to go on.

    Actually, step one: when installing such a wiring harness, for a charger, you want to be careful which wire you connect to pos and neg: there’s only way that’ll work, the other would be tantamount to reverse connecting jumper cables or whatever, smoke fuses.

    I gather you don’t have it installed, or??
     

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    #41 Mendel Leisk, Nov 18, 2023
    Last edited: Nov 18, 2023
  2. Mendel Leisk

    Mendel Leisk Senior Member

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    If the wiring harness is not installed, just do the ohm test at both ends, verify continuity. Maybe mark at both ends with daub of red paint, to keep it straight.
     
    #42 Mendel Leisk, Nov 18, 2023
  3. Mendel Leisk

    Mendel Leisk Senior Member

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    The wiring harness doesn’t have to be installed directly at the battery; it can be at the under-hood fuse box. Connect to pos lead going into fuse box, neg to a bolt somewhere.
     
    #43 Mendel Leisk, Nov 18, 2023
  4. bisco

    bisco cookie crumbler

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    with a digital meter, you'll get a negative if the leads are incorrect, but the value will be the same. you don't need to find a ground on the car, inserting the leads into both sides will work fine, just don't touch them together
     
    #44 bisco, Nov 18, 2023
  5. RTW

    RTW Junior Member

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    But if I touch the meter leads to the wrong ones (positive to negative), won't that cause a short? I need to safely figure out which is positive. And when you say don't touch them together, what exactly do you mean by "them"?
     
    #45 RTW, Nov 18, 2023
  6. RTW

    RTW Junior Member

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    Okay, I'm confused. FYI, the harness is installed on the battery. The photo was from the AC unit cord end. With this ohms thing you mentioned, I'm not sure what to turn my (DT-830) dial to for that? I'm very new to all this. And if I touch the black lead to the negative pin in the harness connected to the battery, when trying to find which is positive, won't that cause a problem?
     
    #46 RTW, Nov 18, 2023
  7. RTW

    RTW Junior Member

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    Okay, I'm confused. FYI, the harness is installed on the battery. The photo was from the AC unit cord end. With this ohms thing you mentioned, I'm not sure what to turn my (DT-830) dial to for that? I'm very new to all this. And if I touch the black lead to the negative pin in the harness connected to the battery, when trying to find which is positive, won't that cause a problem?
     
    #46 RTW, Nov 18, 2023
  8. RTW

    RTW Junior Member

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    Found this online:

    https://www.webbikeworld.com/wp-content/uploads/2014/02/battery-tender-wiring-diagram.jpg

    on this page: https://www.webbikeworld.com/battery-tender-sae-harness-installation/

    I'm guessing this would be the same for all Battery Tenders, including my Junior.

    Follow up: Also found this in a Q&A on the harness page on Amazon:

    Q: Which side of the quick connector is connected to RED, which I assume is positive?
    A: on the quick connector the exposed male terminal is negative, the female is positive
    By Dickiedo in the United States on May 25, 2015See other answers
    Q: Which side of the connector is positive? The exposed conductor?
    A: The RED side is (+)positive. BLACK is (-) Negative. Positive is fused and UNEXPOSED on the rubber connector. The negative lead is exposed on the rubber connector.
     
    #47 RTW, Nov 18, 2023
    Last edited: Nov 18, 2023
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  9. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Nearly any meter you could get these days would just autocorrect and show a negative voltage if you hooked it up backwards. No harm done, you just ignore the minus sign, and for your purposes that would be good enough.
     
    #48 Leadfoot J. McCoalroller, Nov 18, 2023
  10. RTW

    RTW Junior Member

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    Oh, okay, so there's no danger of touching positive to negative and vice versa (by mistake)?
     
    #49 RTW, Nov 18, 2023
  11. bisco

    bisco cookie crumbler

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    no, you can't cause a short if you touch the wrong ones. i mean don't let the meter probes touch each other while in the plug, that would cause a short
     
    #50 bisco, Nov 18, 2023
  12. bisco

    bisco cookie crumbler

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    the female side is positive so you can't accidentally touch it to ground and cause a short.
    on the tender, the male side will be positive because it is protected against accidental shorts
     
    #51 bisco, Nov 18, 2023
  13. Mendel Leisk

    Mendel Leisk Senior Member

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    That’s why I woul recommend only having ONE probe at the connector, positive/positive, and the neg probe touching car body, away from the connector. I’ve done both probes at the connector, and they touched, shorting it. Luckily there was a fuse IN my connector cable, and it blew.
     
    #52 Mendel Leisk, Nov 18, 2023
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  14. RTW

    RTW Junior Member

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    Okay, so I touched the positive probe to the female part of the connector, and the negative to the body of the car, and nothing happened. Then I touched the negative to the male part of the connector, and that got a reading, but it was weird. It showed between 12.4 and 12.8 for a couple seconds, then it steadily started climbing... 13, to 14, and on until it zeroed out. It did this every time I tried. Very strange. Then I plugged in my aux meter, with the key at Aux, and it showed 12.2. The car has been sitting for a few days.
     
    #53 RTW, Nov 18, 2023
    Last edited: Nov 18, 2023
  15. bisco

    bisco cookie crumbler

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    12.2 isn’t bad in auxiliary.
    Sometimes a changing meter is because the probes aren’t making good steady contact
     
    #54 bisco, Nov 18, 2023
    Last edited: Nov 18, 2023
  16. Mr.Vanvandenburg

    Mr.Vanvandenburg Senior Member

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    Why not use a battery monitor?
     
    #55 Mr.Vanvandenburg, Nov 18, 2023
    Last edited: Nov 18, 2023
  17. RTW

    RTW Junior Member

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    One less thing to buy/install/maintain, I suppose.
     
    #56 RTW, Nov 18, 2023
  18. RTW

    RTW Junior Member

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    Glad the 12.2 reading seems ok.

    I don't expect the reading to stay rock solid on the multimeter, but this behavior (steadily climbing until it zeroes out) is bizarre. I just wonder why that's happening. Is it the meter (which seemed fine when I tested the battery at the terminals), or something about the harness? Or maybe this harness and this particular meter just don't get along? Strange...
     
    #57 RTW, Nov 18, 2023
  19. bisco

    bisco cookie crumbler

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    there's no relationship between the meter and the harness, it's just a conduit to the battery, as long as the harness connections at the battery are tight.
    you can test the harness integrity by putting the tender on it and checking the aux meter every 24 hours
     
    #58 bisco, Nov 18, 2023
  20. Mendel Leisk

    Mendel Leisk Senior Member

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    The number goes higher and higher, then displays zero? Try a different meter?

    12.2 is not very good, I’d be thinking about replacement.

    Who installed the harness btw?
     
    #59 Mendel Leisk, Nov 18, 2023
  21. RTW

    RTW Junior Member

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    The OEM toyota battery is supposedly new. The harness was installed by the mechanic. It looks nice and tight to me, and it must be installed correctly, because I ran through a full cycle with the Battery Tender, red light (charging) to green light (charged). The 12.2 reading was from the aux outlet, after the car had been sitting for a few days, not connected to the Tender.
     
    #60 RTW, Nov 19, 2023
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