Prius Gen 2 – SOC drops overnight, normal behavior?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Kamilpcc, Aug 18, 2025 at 11:34 AM.

  1. Kamilpcc

    Kamilpcc New Member

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    Hi everyone,

    I have a 2007 Prius Gen 2 and I'd like to clarify something.

    When I park the car, the MFD usually shows almost all blue bars (sometimes almost green). But when I return a few hours later—or the next morning—the display only shows two purple bars, sometimes almost empty.

    Then, as soon as I drive off, the car rapidly charges the HV battery to the blue bars. This cycle repeats, and because of this, I feel like the gasoline engine is working more often to recharge the battery, which slightly increases my fuel consumption (currently about 5.3 L/100 km).

    So, my questions are:

    Is it completely normal for the display's SOC to drop overnight?

    Is this simply ECU recalibration, and not true self-discharge?

    Could this behavior be related to the age of the HV battery, or simply to the way the Prius manages its buffer (SOC range 40-80%)?

    I'd appreciate it if someone could confirm whether this is normal behavior for the Prius, or if it could be a sign of a weakening HV pack.

    Thanks!
     
    #1 Kamilpcc, Aug 18, 2025 at 11:34 AM
    Last edited by a moderator: Aug 19, 2025 at 2:38 AM
  2. bisco

    bisco cookie crumbler

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    yes
     
    #2 bisco, Aug 18, 2025 at 1:53 PM
  3. Tombukt2

    Tombukt2 Senior Member

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    Very normal behavior mine drops from a full load of green Parked to half blue 50 feet down driveway . But comes right back up immediately on the road even with ac on.
     
    #3 Tombukt2, Aug 18, 2025 at 3:03 PM
  4. pasadena_commut

    pasadena_commut Senior Member

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    Dropping to purple overnight is not normal behavior. If it had some sort of high voltage short there should be a check engine light on, and none was mentioned. The pack is probably weak. If the OP pays for a copy of the Dr. Prius app there is a test that can be run which will give an estimate of the state of the pack.
     
    #4 pasadena_commut, Aug 18, 2025 at 8:18 PM
  5. dolj

    dolj Senior Member

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    ^^^ Agreed. This is not normal behaviour. It can be a sign of a weak hybrid vehicle (HV) battery, so verifing that would be a good idea.
     
    #5 dolj, Aug 18, 2025 at 10:24 PM
  6. Carall

    Carall Member

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    This is a sign of weakening of the HV package, loss of capacity. 3 discharge charge cycles will eliminate this, but how long it will last depends on the condition of the battery.
     
    #6 Carall, Aug 18, 2025 at 10:25 PM
  7. Kamilpcc

    Kamilpcc New Member

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    Okay, I'll buy a Dr. Prius and test the battery. I also noticed that the purple level stays on for a long time while driving, then quickly jumps to blue. Maybe it's because of the short driving distances. Regardless, I'll test it with the Dr. Prius to be sure.
     
    #7 Kamilpcc, Aug 19, 2025 at 8:47 AM
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