Maintaining Battery during dormancy

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by gatorback, Jan 24, 2026 at 10:14 PM.

  1. gatorback

    gatorback Junior Member

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    It is my understanding, when the Prius Gen3 is garaged, it is not off in the truest sense: it is still burning battery energy and will eventually exhaust one or more batteries. This give rise to several questions:

    1) What is the longest period of dormancy possible? Months, weeks?
    2) During dormancy is only the 12V (small battery) exhausted or is the large HV (hybrid battery) drained as well?
    3) If a 12V trickle charger is engaged during dormancy, is this is enough in two maintain both batteries (hybrid HV battery and 12V)?
    4) If parked at the airport for an extended period of time, is it enough to disconnect the 12V battery or is there a need / advantage to disconnecting the HV hybrid battery?

    I have a Nocu Trickle charger that is switched on / off with a wifi smart switch for 1-month dormancy periods.
     
    #1 gatorback, Jan 24, 2026 at 10:14 PM
    Last edited: Jan 24, 2026 at 10:19 PM
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  2. bisco

    bisco cookie crumbler

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    When off, the hybrid battery is isolated from the rest of the car.
    They typically don’t lose much energy, but the older they are, the more prone to it.

    there is a constant drain on the 12v, again, the older it is, the more likely to drain and sulphate.
    In good health, it should last more than a few weeks, but becomes more risky as it ages.
    A maintainer is always best, but disconnecting also works. But you may lose a few settings like radio stations or window memory, it’s inconsistent
     
    #2 bisco, Jan 25, 2026 at 2:22 PM
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  3. VelvetFoot

    VelvetFoot Active Member

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    I don't think there's a need to cycle that maintainer manually.
     
    #3 VelvetFoot, Jan 25, 2026 at 2:50 PM
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  4. bisco

    bisco cookie crumbler

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    correct, it does all the switching itself. when not charging, it is monitoring charge level. you don't want to switch it off
     
    #4 bisco, Jan 25, 2026 at 8:05 PM
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