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12V battery and Charging

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Alan Sailer, Mar 29, 2022.

  1. Alan Sailer

    Alan Sailer Junior Member

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    Vehicle:
    2007 Prius
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    One
    Hello,

    I am just looking for some general instructions on troubleshooting a possible 12V battery issue.

    Some background: About half a year ago I was having some trouble with the car and as part of the solution I changed out a 12V battery that seemed iffy. Recently I have noticed that my displays clock/instruments/display are getting intermittently dim. The internal battery check showed that the 12V battery was not good. 12.2V/11.9V
    unloaded/lights on.

    This morning the displays all looked good. Battery was 14.4/12.1. Driving away the charging voltage was 14.1-14.0V. When I got to work (20min drive) the battery was 12.8V/12.3V.

    I am trying to find out a good scheme to follow for troubleshooting this problem. I suppose a six month old battery could be going bad but this seems unlikely.

    Thanks in advance for any comments.
     
    #1 Alan Sailer, Mar 29, 2022
  2. ChapmanF

    ChapmanF Senior Member

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    Vehicle:
    2010 Prius
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    IV
    If you're relying on the voltage shown on the Vehicle Signal Check screen of the MFD, on every Prius where I have ever made this comparison, that reading is a substantial fraction of a volt lower than what you would see at the battery (or even right nearby, say at pin 16 of the diagnostic port). It is probably the accurate voltage at whatever internal point of the MFD supplies the measurement.

    Accordingly, the numbers you are giving here, if I saw them in my car on the MFD, I would consider reasonably good. They wouldn't give me any concern about the battery.

    I am puzzled by your 14.4/12.1. It would surprise me to see anything as high as that first number, except when the car is showing READY (in which case, it is not really a battery measurement anymore).
     
    #2 ChapmanF, Mar 29, 2022
  3. Alan Sailer

    Alan Sailer Junior Member

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    Vehicle:
    2007 Prius
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    One
    Chapman,

    My error. Should be 12.4/12.1. I am feeling bad this morning and made an error.

    If the drop is that high then maybe I will monitor at the battery.

    I am still puzzled by the brightness shift. I'm understanding the automatic dimming with the light on during day/night. This is something different.
     
    #3 Alan Sailer, Mar 29, 2022
  4. ChapmanF

    ChapmanF Senior Member

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    What happens if, for experimental porpoises, you turn the panel dimmer knob all the way up till it clicks?
     
    #4 ChapmanF, Mar 29, 2022
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