1. Attachments are working again! Check out this thread for more details and to report any other bugs.

is my 12v battery really dying?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Quickie, Dec 20, 2018.

Tags:
  1. Quickie

    Quickie New Member

    Joined:
    Dec 19, 2018
    5
    2
    0
    Location:
    Seattle
    Vehicle:
    2008 Prius
    Model:
    Three Touring
    My car says my battery is fine. It meets the minimum voltage requirements in all modes. It is exactly 12v for instance when the battery is on. And 14v in ready mode. Maybe it's dipping occassionally? The problem is my car doesn't start and the clock resets. Is it possible that the battery is going bad but most of the time works well enough to pass diagnostic tests? Thanks in advance.
     
  2. SFO

    SFO Senior Member

    Joined:
    Feb 7, 2017
    5,286
    4,225
    0
    Location:
    Northern California
    Vehicle:
    2007 Prius
    Model:
    N/A
    Welcome to PriusChat!!

    12v is generally considered low for an AGM battery.

    Grab a multimeter and check the jump points under the hood, don't rely on the diagnostic tests.

    When was the last time it was changed, and how often to do you drive (example: 1 hr per week) ?

    Cool screen name :whistle:
     
    Raytheeagle likes this.
  3. Mendel Leisk

    Mendel Leisk Senior Member

    Joined:
    Oct 17, 2010
    54,473
    38,103
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    Not sure what you mean by "on". How are you measuring voltage, via the car's displays? If so, that will maybe depress voltage slightly.

    A more accurate voltage reading would be with a separate multimeter, preferably digital, while the car is off. If you get 12.0 volts by that method, yeah: that's a near-dead battery:

    [​IMG]

    (the above chart is for conventional flooded acid 12 volt; the AGM style used in Prius should read 0.1~0.2 higher)

    Pick up something like a Solar BA5 and you can see for yourself how it is.



    First question last: how old is it?
     
  4. padroo

    padroo Senior Member

    Joined:
    Jan 11, 2008
    2,763
    2,250
    13
    Location:
    Chesterton, Indiana Another third world country.
    Vehicle:
    2016 Prius
    Model:
    Four
    12 Volt battery problems are probably the number one question on Prius Chat.
     
    jerrymildred likes this.
  5. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    107,571
    48,862
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    and the number one answer :D
     
    SFO and Raytheeagle like this.
  6. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    107,571
    48,862
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    welcome!

    very possible.
    check the connections for tightness and cleanliness, especially negative to ground.
     
  7. Quickie

    Quickie New Member

    Joined:
    Dec 19, 2018
    5
    2
    0
    Location:
    Seattle
    Vehicle:
    2008 Prius
    Model:
    Three Touring
    Thanks. I took it in to the Toyota dealership and they told me the battery was bad. I changed it but many of the screws were stripped so I had to take the thing next to the battery out in an unconventional way. What is that thing called? Usually they suggest taking the 12mm screws out to remove it, but since they were stripped I took out the side screws. At any rate I couldn't get the back screws in because of the angle. I took it back to Toyota and the mechanic said everything's secure. But I still feel uncomfortable not having those screws in. Especially since I don't even know What's not screwed in.
     
    SFO likes this.
  8. Quickie

    Quickie New Member

    Joined:
    Dec 19, 2018
    5
    2
    0
    Location:
    Seattle
    Vehicle:
    2008 Prius
    Model:
    Three Touring
    Thanks for the chart... And it was low. Got a new Battery.
     
    Mendel Leisk likes this.