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What's your 12v battery resting voltage?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Doug Pinkerton, Oct 4, 2024 at 9:41 AM.

  1. Doug Pinkerton

    Doug Pinkerton Junior Member

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    2013 Prius
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    Two
    I recently replaced a two year old Diehard battery (under warranty) that was showing 11.9 in the morning on the Signal Info portion menu of the Prius . I happened to check that menu as I was experiencing some odd behavior and read that a low 12v can cause a variety of odd behavior.

    Two weeks later and the new 12v is also reading 11.9 in the morning. At the battery itself, I get about 12.2.

    According to everything I've read here on Prius Chat and elsewhere those numbers point to a poor battery.

    Having a battery "fail" after just two years and brand new one apparently having issues within two weeks, I was concerned that something funny might be going on and I decided to go my Toyota dealer to have them test the battery and check for parasitic draw.

    They told me parasitic draw was well within norm (under 50 mA). The battery failed their test. Printout from test shown here.

    However, there is a note on my work order, in reference to my mentioning the 11.9 displayed in Signal Info, that reads:

    "Resting voltage of 11.9 is completely normal on a hybrid vehicle as compared to other hybrid models"

    This is very interesting to me. While it goes against everything I've found related to healthy voltage, it does seem to align with things I've read about the Prius's charging of the 12v being low on its priorities.

    Can anyone check their resting and tell me if it aligns with what the tech said?

    While I'm happy that there does not to be something weird going on with the car, I'm not certain why my brand new replacement battery is failing and I'm confused by conflicting opinions on "normal" resting voltage.

    Thanks!
     

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  2. Tombukt2

    Tombukt2 Senior Member

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    The statements wording of English doesn't even make sense even as poor as my English might be something about the resting rate is normal for a Prius hybrid vehicle versus other hybrid vehicles yeah okay whatever I know in my vote which is another hybrid vehicle unlike the Prius not the same kind hybrid synergy drive or whatever and I don't see anything about its 12 volt resting voltage being below 12 volt I measure at the battery I don't care what it is after it comes down the pipeline through all the wiring I expect them one volt voltage drop pretty easily I would imagine but what it's sitting in the back of the car and it's fully charged state resting state after charging whatever you want to call it needs to be 12 volts now what the car sees after it comes down the line I'm not sure if that's a bad thing or not as long as it stays right at 12 volt 11.9 etc problems generally aren't supposed to develop until we have a full voltage dropper better You see things talked about it 10 volts and 9 point something volts and so on Not in the Prius but in other 12 volt systems My car used to start a regular starter with 10 and 1/2 volts in the battery according to the fancy expensive test meter.
     
  3. StarCaller

    StarCaller Senior Member

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    12.7v since 10 years /
     
  4. bisco

    bisco cookie crumbler

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    is it an agm battery? mine was always around 12.7 in the morning, until it croaked