What is a normal rate of discharge for the 12v battery?

Discussion in 'Gen 5 Prius Care, Maintenance and Troubleshooting' started by FatCat0, Feb 19, 2025.

  1. FatCat0

    FatCat0 New Member

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    Given all of the controversy over this (potential) issue, I'm curious: what is a normal rate of discharge? My battery was at 12.8V when I turned it off after driving last night (9 pm), slowly fell to 12.56 by 10:30 this morning, car not plugged in during this period. That seems like a pretty significant drop, but admittedly I've literally never tracked my battery voltage before now.

    So, what is normal? A couple tenths of a volt a day? Faster drop-off initially, then it tapers off? What's the absolute lowest voltage one should consider "acceptable" before taking the effort to get it topped back up?
     
    #1 FatCat0, Feb 19, 2025
  2. bisco

    bisco cookie crumbler

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    Idk, but the best test you can do is when you get home, wait a few hours for the surface charge to wear off, then check the voltage.
    Or you could turn the headlights on for a few minutes.
    Leave the hood unlatched so you don’t have to open a door in the morning, and check the jump point for voltage.
     
    #2 bisco, Feb 19, 2025
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  3. Fenichel

    Fenichel Junior Member

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    When I looked into this a while ago, the drop seemed to be exponential decay (faster at first, then slower), with a projected half-life of close to 2000 hours. Of course, I never actually allowed the voltage to get much lower than 12V.
     
    #3 Fenichel, Feb 19, 2025
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  4. schja01

    schja01 Senior Member

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    If I leave the hood unlocked and I get a warning on the MID until I close it. I mean it remains forever. 2024 Prius (not prime) limited.
     
    #4 schja01, Feb 19, 2025
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  5. bisco

    bisco cookie crumbler

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    that's a nice safety feature we didn't have in past generations
     
    #5 bisco, Feb 19, 2025
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