2020 Prime - died!

Discussion in 'Prime Care, Maintenance and Troubleshooting' started by DicCarlson, Dec 23, 2025.

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  1. DicCarlson

    DicCarlson New Member

    Joined:
    Dec 23, 2025
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    Location:
    North River, NY
    Vehicle:
    2020 Prius Prime
    Model:
    Plug-in Base
    Car was plugged in to charge the traction battery. I went out to start the car while it was plugged in and went back about 15 minutes later to shut it off. Well, it was off and wouldn't start - 12V battery dead! Jump started and it ran fine and still starts a day later.
    What happened here??
     
    #1 DicCarlson, Dec 23, 2025
  2. Groovekin

    Groovekin Junior Member

    Joined:
    Nov 4, 2014
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    Location:
    Denver
    Vehicle:
    2011 Prius
    Model:
    Two
    Same issue. Had it plugged in for a long time which someone said can drain the 12volt. Had auto store test battery and said it was bad.
    I assume there's an alternator for charging it but not sure and I also thought there was a way to force the ICE to run to test it but couldn't find it. Charge will hold after trickle charge for a day or two. Maybe 5 years on the battery is not too bad??
     
    #2 Groovekin, Dec 23, 2025
  3. David Lopez

    David Lopez New Member

    Joined:
    Jan 3, 2026
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    Location:
    85143
    Vehicle:
    2026 Prius Plug-in
    Model:
    Plug-in Base
    My battery died the same way, found out it was something I left plugged into the fuse box. The battery could just be old or a dud.
     
    #3 David Lopez, Jan 7, 2026
  4. EchoEcho

    EchoEcho Junior Member

    Joined:
    Dec 8, 2020
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    Location:
    Ontario
    Vehicle:
    2017 Prius
    Model:
    Technology
    Car will not enter READY mode while plugged in for charging, therefore turning the ignition on is running everything on the 12v battery alone. Once it is dead, there isn't enough power the start the computers, converter, etc.

    Jumping gets you back up and running then converter charges your 12v back up.

    Now that you've been though a hard discharge, suggest you keep an eye on that 12v battery health.
     
    #4 EchoEcho, Feb 27, 2026 at 7:55 PM
  5. Prodigyplace

    Prodigyplace 2025 Camry XLE FWD

    Joined:
    Nov 1, 2016
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    Location:
    Central Virginia
    Vehicle:
    Other Hybrid
    Model:
    XLE
    When in READY mode and not in Neutral, the 12v battery is charged from the traction battery through the inverter.
     
    #5 Prodigyplace, Feb 27, 2026 at 8:00 PM
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