12V Battery Voltage in Diagnostic Display -- New Battery Needed?

Discussion in 'Prius c Care, Maintenance and Troubleshooting' started by Dogwood2, Apr 27, 2020.

  1. Dogwood2

    Dogwood2 Member

    Joined:
    Feb 15, 2013
    106
    47
    0
    Location:
    California
    Vehicle:
    2013 Prius c
    Model:
    Three
    I know a typical 12V battery is good for maybe four to six years, and mine is older than that, unless I'm forgetting that I replaced it. I recently discovered the "Diagnostic Mode", which you get to by putting the car into "Run" mode (in this case without turning on the engine) and then holding down the "Car" button on the display while rapidly switching the headlights on and off three times. If you've never done this, give it a try.

    The battery voltage is displayed in the "Vehicle Signal Check" section. In my case, the display shows 11.9V or 11.8V while the engine is off. If I turn on the engine, this jumps to 14V as the engine and traction battery charge the 12V battery.

    PriusC2b.jpg
    If anyone has a new 12V battery, what numbers do you see? My general understanding is this 11.9 I'm seeing is pretty low, and a new battery would show a number in the high 12's, so it's time for the replacement. (I might expect the system would warn us that the battery is low, rather than waiting for us to check it, but I guess that's not the case.)

    FWIW, this YouTube video shows someone replacing his battery, and it seems pretty straightforward. If the dealer is asking $100+ labor to do this, I should be able to do it myself.
     
    bisco likes this.
  2. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    90,026
    40,383
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    new is around 13 volts. are you driving much? maybe charge it up and keep an eye on it

    i think there is a 12v warning, but doesn't seem to work well. the fact that your car starts may be the problem :cool:
     
  3. cutter44

    cutter44 Member

    Joined:
    Apr 19, 2015
    196
    48
    0
    Location:
    MA
    Vehicle:
    2012 Prius c
    Model:
    Four
    I bought a new battery from the dealer a few weeks ago and checked it before I installed it and it showed 12.55v with a multimeter.
     
    bisco likes this.
  4. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    90,026
    40,383
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    put a charger on it, then see what it holds at over time.
     
    AlphaFox likes this.
  5. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    10,312
    7,584
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    The number shown on the MFD tends to be a good fraction of a volt lower than what you would see with a meter on the battery itself.

    The numbers you are showing are pretty much comparable to what I was seeing for the last four years of the ten year life of the battery I just replaced (I'm not saying the numbers were higher for the first six years, I just didn't own the car then), and I'm pretty sure if I walked outside right now and checked with the one I put in brand new this winter, it would look pretty much the same.

    Edit: just for grins, I did exactly that, and mine read 11.2 on the MFD in accessory mode, rising to 14 once in READY.

    I did not bother with a meter on the battery itself, but my ScanGauge (which sits within inches of the MFD, but is measuring the voltage on a different circuit, the one that comes to pin 16 of the DLC3 port) was reading pretty much exactly 0.7 V higher than the MFD the whole time.

    If your battery isn't giving you some actual reason to worry about it, I'd probably worry about something else.
     
    #5 ChapmanF, Apr 30, 2020
    Last edited: Apr 30, 2020
  6. Mendel Leisk

    Mendel Leisk Senior Member

    Joined:
    Oct 17, 2010
    40,885
    29,350
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    Best to read independent of the car's displays, at least the voltage, with a multimeter, or better: voltage and CCA with electronic load tester. Just happened to be doing the latter today:

    IMG_2310.JPG IMG_2312.JPG
    IMG_2313.JPG
    Automotive retailers selling batteries will often have pro-level testers of this ilk, and will test for free.
     
Loading...