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12V Battery Died, Now What?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Gunnar Boag, May 11, 2024.

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  1. Gunnar Boag

    Gunnar Boag Junior Member

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    Yesterday my 2008 12v died on me. Someone must have bumped into my car when I was away, because apparently the alarm had been going for 15 minutes and killed the 12v. A friendly stranger jumped us and got us on our way fortunately.

    Here is my question, is my 12v going to be seriously damaged from this? I haven’t had any issues with slow starts or dim lights since, but I worry that the hybrid battery will be focusing a lot on charging the 12v if it is damaged and won’t hold a charge as well. The hybrid battery seems to drop a bar a little easier now, but we are also starting to use the AC as of yesterday. Has anyone had any problems after their 12v was drained on accident?

    My plan is to take it to Les Schwab to get a battery health check up, but I figured I would ask the pros before.
     
  2. mr_guy_mann

    mr_guy_mann Senior Member

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    A number of things can cause the alarm to trigger, such as a glitchy door latch or something preventing the tailgate from closing fully.

    That said, the 12V battery shouldn't be "dead" after 15 minutes. If it's 5 years or older, I would suggest just replacing it and having the car tested for excessive key off (parasitic) draw.

    Also, how is the car used? If it sits for too long or only for short trips, then there might be enough run time to properly charge the 12V battery.

    Posted via the PriusChat mobile app.
     
  3. Gunnar Boag

    Gunnar Boag Junior Member

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    Yeah I was surprised the alarm going off did that much damage to it, and now I'm guessing it did some pretty good damage to an already weakened battery. I'm not sure how old it is because I bought it used, but probably around four to five years old.

    The car is used for a mixture of short commutes and longer drives. I have driven it for a handful of 30 minutes drives since it died. One thing I noticed is that there is an intermittent "whirring" noise that happens now while I'm driving. I read somewhere that this is a sign the 12v is on it's way out...any thoughts on that?
     
    #3 Gunnar Boag, May 12, 2024
    Last edited by a moderator: May 22, 2024
  4. bisco

    bisco cookie crumbler

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    is the noise coming from under the hood, might be the brake actuator.

    the 12v doesn't do anything when the car is ready. the inverter/converter runs all the 12v accessories and keeps the 12v charged.
    get the load test, then you'll know.
    the battery has a date code on top, but you have to remove all the junk in the way.
     
  5. Gunnar Boag

    Gunnar Boag Junior Member

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    After doing some research on the actuator, the noise is definitely that. However, I'm not sure if it is happening more frequently or I am just now noticing it because of the battery dying. Hopefully the actuator isn't starting to go because I just replaced the HV battery and would hate to drop another 2-3 grand on this car...
     
  6. bisco

    bisco cookie crumbler

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    a weak 12v will cause the pump to run more slowly and seemingly noisier when you open the drivers door to get in.
    but when in ready, it has plenty of power. a lot of us will imagine something has changed when something is wrong, but usually, we're just paying more attention.
     
  7. mr_guy_mann

    mr_guy_mann Senior Member

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    With the car "ready", step on the brake pedal several times until you hear the noise. Then leave the pedal alone and just wait (time it) until you hear it again. If you do.

    On a "good" car, it can take what, an hour + of just sitting for the brake system to lose pressure enough to trigger the pump.

    If there is an internal leak in the actuator assembly that bleeds off pressure quicker, that can cause the pump to cycle every few minutes or more often.

    Posted via the PriusChat mobile app.