battery issue? Left my prime parked for 2.5 weeks

Discussion in 'Prime Care, Maintenance and Troubleshooting' started by GeoJ, Nov 13, 2025 at 10:51 PM.

  1. GeoJ

    GeoJ Active Member

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    Vehicle:
    2023 Prius Prime
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    XSE
    I left my car for 2.5 weeks, have 21 miles on the EV when I returned.

    Drove it once, started fine, and then drove a mile to another place and parked. Now car won't start, dead battery? My bad (very bad, after a 24 hour plane trip, so a bit out of it), I think it is possible I left the car on after I drove it the second place a mile down the road. So if I left it on would that cause the 12V battery to run down, or is it that I left it for 2.5 weeks, or something else why car won't start? Any thoughts for this travel zombie? Thanks
     
    #1 GeoJ, Nov 13, 2025 at 10:51 PM
  2. BiomedO1

    BiomedO1 Senior Member

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    It probably just needs a jump start.
    Get the battery checked-out tomorrow. I'm assuming the car wasn't plugged-in and charging that entire time. That will draw down the 12VDC battery too.
     
    #2 BiomedO1, Nov 13, 2025 at 11:21 PM
  3. GeoJ

    GeoJ Active Member

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    Thanks, I will try to jump start it. I assume just plugging it in now, from what I've read online, won't get the 12V to a level to start the car. Yes, it was not plugged in the entire time.
     
    #3 GeoJ, Nov 14, 2025 at 12:15 AM
  4. BiomedO1

    BiomedO1 Senior Member

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    While your traction battery is charging; portions of your 12VDC systems are energized to ensure power to ECU & cooling fans; it's not really designed to provide a 'recharge' of your 12 VDC battery - though it does get some voltage in the process.
    I believe that your 12VDC battery is below 10.5 VDC, that's about the voltage the can't close the relays to engage the DC-DC converter, pot the car into ready mode. I need to put my gen4 on a battery charger about once a year, when I find it below 11.5 VDC - car still goes into ready mode at that level.
    I didn't have this problem when my car was a daily driver, but now that I'm retired and only drive a few times a week, I've noticed the battery getting low and I do unplug the car when the battery is finished charging.
     
    #4 BiomedO1, Nov 14, 2025 at 3:19 AM
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