What happens when you disconnect the battery?

Discussion in 'Gen 5 Prius Technical Discussion' started by Paul Gregory, Jul 6, 2026 at 11:42 PM.

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  1. Paul Gregory

    Paul Gregory Senior Member

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    Numerous people have suggested I use a battery disconnect to resolve my parasitic drain problem.
    Here's what happened when I didn't drive the car for 3 days, and the voltage fell below 5V:

    Here's an excerpt from the email I got:
    The primary driver for the 2024 Toyota Prius Prime XSE has been updated. The vehicle has been removed from your Toyota account and any active subscriptions, services, and reservations have been cancelled. If applicable, any Digital Keys or shared Digital Keys for this vehicle have also been disabled.

    When your vehicle was removed from your account, by default the vehicle was reverted to Privacy Mode where a limited set of data, including location data, remains transmittable when you press the SOS button in your vehicle and to enable Safety Connect features (includes automatic collision notification, emergency and roadside assistance, and stolen vehicle services). For more information, please refer to the Connected Services Privacy Notice.

    I had to call the Toyota support line, and now I have a job ahead of me to sign back in through the app.
     
    #1 Paul Gregory, Jul 6, 2026 at 11:42 PM
  2. bisco

    bisco cookie crumbler

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    someone just posted that they are on their 4th 12v on a 2025
     
    #2 bisco, Jul 7, 2026 at 2:23 PM
  3. Paul Gregory

    Paul Gregory Senior Member

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    Makes you wonder why someone repeats the same action, expecting a different result.
     
    #3 Paul Gregory, Jul 8, 2026 at 2:39 PM
  4. bisco

    bisco cookie crumbler

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    no place to plug in a maintainer, seems at a loss. dealer told him to drive it more. why would I buy a car to save fuel, and drive it more than I need to?
     
    #4 bisco, Jul 8, 2026 at 8:29 PM
  5. Paul Gregory

    Paul Gregory Senior Member

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    Can't imagine.
     
    #5 Paul Gregory, Jul 8, 2026 at 10:14 PM
  6. bisco

    bisco cookie crumbler

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    can't imagine finding out you bought the wrong car for your situation after the fact
     
    #6 bisco, Jul 9, 2026 at 1:12 PM
  7. Paul Gregory

    Paul Gregory Senior Member

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    I don't ditch the whole car because I might be disappointed with one design flaw.
    I don't want to lose $20,000.
     
    #7 Paul Gregory, Jul 9, 2026 at 2:41 PM
  8. bisco

    bisco cookie crumbler

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    exactly, that's the problem
     
    #8 bisco, Jul 10, 2026 at 4:01 PM
  9. Paul Gregory

    Paul Gregory Senior Member

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    If I'm hearing right, one unfixed problem means ditch the car,
    regardless of the expense. No thanks.
     
    #9 Paul Gregory, Jul 10, 2026 at 5:14 PM
  10. bisco

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    no, too expensive. unless Prius go up in value instead of down. it's been known to happen.
    but what a bitter pill to swallow.
     
    #10 bisco, Jul 10, 2026 at 9:41 PM
  11. Mendel Leisk

    Mendel Leisk MMX GEN III

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    We were looking for excuses to drive, to keep the battery happy, and then started thinking "this is nuts". Current situation:

    IMG_4315.jpeg

    Working well, current battery was installed in September of 2015.
     
    #11 Mendel Leisk, Jul 11, 2026 at 11:18 AM
  12. bisco

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    I wonder if a solar panel would work in a no outlet situation
     
    #12 bisco, Jul 11, 2026 at 1:28 PM
  13. ChapmanF

    ChapmanF Senior Member

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    Worked well for me on a former vehicle. An off-the-shelf solar maintainer product with (IIRC) a five-watt panel did the trick. The panel was about one square foot, and this was nearly 20 years ago.
     
    #13 ChapmanF, Jul 11, 2026 at 1:47 PM
  14. Mendel Leisk

    Mendel Leisk MMX GEN III

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    #14 Mendel Leisk, Jul 11, 2026 at 1:48 PM
  15. ChapmanF

    ChapmanF Senior Member

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    If that's 2.4 amps at 12 volts, that's like 29 watts, or I think about six times what I had. (But then, my much older vehicle may have had much lower quiescent load than a modern Prius.)
     
    #15 ChapmanF, Jul 11, 2026 at 1:51 PM
  16. Paul Gregory

    Paul Gregory Senior Member

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    There is considerable variance in the quality of 12V FLA batteries. My VW still has the original 9 year old battery, showing no signs of degradation. As a child on the farm I recall that some of the batteries lasted 20 years.

    Nowadays, most cheap replacement batteries use recycled lead "foam" which may deliver the claimed CCA, but not for long. Some companies are selling lead acid batteries made from "virgin lead," but they are generally in the $200 range.
    I would likely opt for lithium technology, but I don't know if I can leave the BMS wires disconnected if I were to use a lithium replacement.

    Has anyone had success replacing the OEM battery with a non-OEM?
     
    #16 Paul Gregory, Jul 11, 2026 at 2:29 PM
    Last edited: Jul 11, 2026 at 2:38 PM
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