Checking 12v battery from headunit (video)

Discussion in 'Gen 3 Prius Main Forum' started by abubin, Aug 19, 2020.

  1. abubin

    abubin Member

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    Here is a simple and quick video on self checking the 12v battery for those who have a headunit.


     
  2. ASRDogman

    ASRDogman Senior Member

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    12.2v is not okay. It's low.
    That sure looks strange with the steering wheel on the right hand side! :)
     
  3. Grit

    Grit Senior Member

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    That’s because the proper way to measure is from the jump points under the hood without a load. The method above will cause everyone to hit the panic button and replace their 12 v bat.
     
  4. ASRDogman

    ASRDogman Senior Member

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    I guess... I seem to recall someone said reading it that way it will always be lower.
    It seems easier to just pop the hood and put a meter on it. It would be faster! :)
     
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  5. Grit

    Grit Senior Member

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    Some people don’t even have “time” to open the hood to check their oil level, what are the chances of them finding their multi meter, opening the fuse box and tap on the jump points? And the do the reverse once done? That’s some valuable Netflix time man :ROFLMAO:
     
    #5 Grit, Aug 19, 2020
    Last edited: Aug 19, 2020
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  6. abubin

    abubin Member

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    12.2v is fine. Not great but good enough that you don't need to start looking for replacement. Correct me if I am wrong, I think the 12v battery is not needed for starting the engine. The HV battery take cares of it once that car is in READY mode. Would love to get my hand on a faulty battery that won't start the car so that I can measure to voltage to see what is a dead voltage level.
     
  7. Grit

    Grit Senior Member

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    Pull the 12v lead off the battery and try to put the car on ready. Let us know what happens.
     
  8. ChapmanF

    ChapmanF Senior Member

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    Yeah, in every Prius where I've checked, it has been lower by, like, 0.6 or 0.7 V ... but not changing very much for a particular car, so noticing the difference once and just doing some quick mental arithmetic later isn't much trouble.

    That means if I ever went out some morning and read my car at 12.2 on the MFD, I would be camped out at night trying to see who's been sneaking around and charging my battery. (It better not be the same clown who keeps leaving the zucchini in the back.)
     
    #8 ChapmanF, Aug 20, 2020
    Last edited: Aug 20, 2020
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  9. abubin

    abubin Member

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    Just made a quick check using multimeter.

    multimeter: 12.38
    headunit: 12.1

    Knowing this mean, we can quickly do a calculation when measure using the headunit. For tmes when we are on the road or not having a multimeter available. This is good enough for some reference.

    Thanks for sharing. As always great community here.
     
  10. Salamander_King

    Salamander_King Senior Member

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    I use a BlueTooth battery monitor II permanently installed on the 12v battery posts in my Prius Prime. With Covid-19 restriction, I am not driving my car much. I could pop the hood and check the 12v battery with a DMM, but with this device, I get daily notification and 24/7/365 monitoring from the comfort of sitting on a couch. I don't let my 12v battery go below 12.4v. I charge promptly with a smart charger when my phone notifies me.

    upload_2020-8-20_10-10-54.png
     
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  11. davecook89t

    davecook89t Senior Member

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    For others who might be interested in getting one, what is the make and model of the particular device you are using?
     
  12. Salamander_King

    Salamander_King Senior Member

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    QUICKLINKS Bluetooth 4.0 Battery Monitor II
    Bought the first one ~$30 on Amazon that I am using on PRIME, and bought another one ~$18 from AliExpress I am using on another car. There are few other models and makes available that does the same thing.
    upload_2020-8-20_10-55-26.png

    The accuracy is within 0.05V compared to Fluke DMM. It reads the voltage of 12v battery every 2 min and store the data inside for 30 days. But the data can be synced to phone App as many times as you want and if you sync at least once every 30 days, the data will be stored in the phone app indefinitely. It is very convenient to be able to check when I last charged the 12v and how low or high it was while I am driving or working on the car.
    upload_2020-8-20_10-52-48.png
     
    #12 Salamander_King, Aug 20, 2020
    Last edited: Aug 20, 2020
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  13. Johnny Cakes

    Johnny Cakes Senior Member

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    Abubin, you are correct. The traction battery supplies voltage to "crank" the engine.
     
  14. ChapmanF

    ChapmanF Senior Member

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    Grit was being tricksy there. Although the 12 volt battery is not used to start the engine, it is the car's only source of power until it is made READY, which means you won't be able to READY the car if the 12 volt battery is disconnected ... an impeccably true statement, though a little bit sideways from what abubin was asking.

    If you get the car into READY mode and then unhook the 12 volt battery, the car will stay in READY mode, stopping and cranking the engine as often as it likes. (Of course if you push the off button in that condition, everything will go dark a lot more instantly than you're used to.)
     
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