I have an idea...

Discussion in 'Gen 5 Prius Accessories and Modifications' started by Paul Gregory, Sep 21, 2025 at 1:59 AM.

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  1. Paul Gregory

    Paul Gregory Senior Member

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    ...for which I expect to be attacked. But here it is: Since I have had quite a bit of trouble with dead batteries lately, I'm considering mounting a jump starter pack to my 12V system. I could figure out a way of triggering it remotely, either with a pushbutton, of some other solution. As it stands, I am connecting a jump pack under the hood as needed, but to serve my lazy streak, I'd like to make it easier, without opening the hood and removing the cover off the fusebox. Ideally, it should sense the undervoltage condition, and be triggered automatically by touching the starter button. But because of a number of unknowns, I think I'd like to avoid this option.

    I have located a jumpstarter that has a power switch, so I might be able to mount it in the driver space, connected through the socket power lead, to a live auxiliary socket which I have protected with a circuit breaker. I think it could work.

    What do you think? I don't mind criticism, but I don't need the insults, thanks.
     
    #1 Paul Gregory, Sep 21, 2025 at 1:59 AM
  2. frodoz737

    frodoz737 Top Wrench

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    If that is something you want to try...go for it. However, if this was my vehicle I would fix the problem or sell if it can't be fixed.
     
    #2 frodoz737, Sep 21, 2025 at 2:18 AM
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  3. Paul Gregory

    Paul Gregory Senior Member

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    Battery drain seems to be a persistent problem with my type of vehicle. I have addressed it with several dealers, and it's apparent that nothing more can be done. Sometimes the car can be parked for several days with enough battery to start the car, and other times, it has gone flat in as little as 2 hours. When I say "flat," the voltage only has to drop below about 11.5V, which renders the car disabled, requiring a boost or a service call. Several people have stupidly suggested that replacing the battery will fix it, but I have made it abundantly clear that doing so solves nothing.

    I consider it a design flaw that no way has been devised to tap into the enormous power reserve of the hybrid battery, to activate the DC-DC converter, so that the car can start. I've given up on trying to engineer a solution along these lines. I carry a jumper pack at all times, but I'd like to wire it in such a way that I don't have to go under the hood to hook it up.
     
    #3 Paul Gregory, Sep 21, 2025 at 5:14 AM
  4. Brian1954

    Brian1954 Senior Member

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    Here we go again with another thread about the 12v battery problem in your Gen 5 Prius. This thread will probably end up being locked like the last thread, https://priuschat.com/index.php?posts/3560590

    If you are not willing to buy a new 12V battery, you will need to keep using the jump starter to get the car started.

    Out of curiosity, is the battery-isolator cut-in voltage still set at 12.1V, or did you change it?

    Edit: How are you going to keep the jump starter charged when it goes "flat" without opening the hood?
     
    #4 Brian1954, Sep 21, 2025 at 9:08 AM
    Last edited: Sep 21, 2025 at 9:27 AM
  5. ETC(SS)

    ETC(SS) The OTHER One Percenter.....

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    I think you conflate criticism with insults, and you need to have thicker skin, but to answer your question....

    Look for a WiFi connected 5-12 VDC relay module.
    There about a zillion of them out there and you can graft one onto your jump starter fairly easily.
    I use Shelly and Sonoff - but there are others out there.
     
    #5 ETC(SS), Sep 21, 2025 at 9:19 AM
  6. Paul Gregory

    Paul Gregory Senior Member

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    You are once again being obtuse to the fact that replacing the battery has no effect on the problem. The definition of insanity, as they say...
     
    #6 Paul Gregory, Sep 21, 2025 at 9:41 AM
  7. Paul Gregory

    Paul Gregory Senior Member

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    Obviously, reading my posts before offering advice is not everyone's cup of tea.
     
    #7 Paul Gregory, Sep 21, 2025 at 9:45 AM
  8. Brian1954

    Brian1954 Senior Member

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    I have an idea... how to solve the 12V battery problem in about 30 minutes.

    1. Remove the battery-isolator and the other 12V battery that you installed.
    2. Do not connect the little 12V powered refrigerator unless the car is in "Ready".
    3. Remove any other item that you added to the car's 12V system except for the NOCO Genius 5 battery charger.
    4. Buy a new 12V battery and replace the existing 12V battery.
    5. Drive your car a minimum of 2 to 3 times a week or use the battery charger when you do not drive the car that often.

    I am 99% certain that the 12V battery drain problem will be solved.

    Like post #2 says, you should fix the problem, but you can do whatever you want with your car.
     
    #8 Brian1954, Sep 21, 2025 at 9:58 AM
    Last edited: Sep 21, 2025 at 11:29 AM
  9. Brian1954

    Brian1954 Senior Member

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    Yes, I acknowledge that I missed the part about the jump starter being mounted in the "driver space".
     
    #9 Brian1954, Sep 21, 2025 at 11:45 AM
  10. Mendel Leisk

    Mendel Leisk MMX GEN III

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    You're essentially adding another battery. That's 3 now?
     
    #10 Mendel Leisk, Sep 21, 2025 at 11:49 AM
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  11. Paul Gregory

    Paul Gregory Senior Member

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    Is that the problem? Or is it not being able to start the car?
     
    #11 Paul Gregory, Sep 21, 2025 at 12:16 PM
  12. Paul Gregory

    Paul Gregory Senior Member

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    I think you also missed that replacing the battery has nothing to do with the problem.
    I only mentioned it about 20 times.
     
    #12 Paul Gregory, Sep 21, 2025 at 12:18 PM
  13. Brian1954

    Brian1954 Senior Member

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    In your opinion, " replacing the battery has nothing to do with the problem ". I do not agree with your opinion.

    Until you replace the battery and do the other things I listed in post #8, you will always need a jump starter to start your car. Permanently connecting a jump pack to your car is only a bandaid. Again, you can do whatever you want with your car.
     
    #13 Brian1954, Sep 21, 2025 at 12:32 PM
  14. Paul Gregory

    Paul Gregory Senior Member

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    The problem appeared in the first week I owned the car.
    The dealer tested the battery, and declared that it was OK.
    A second dealer replaced the battery, and it made no difference.

    Do you still disagree that a new battery is not the solution?
     
    #14 Paul Gregory, Sep 21, 2025 at 12:35 PM
  15. Brian1954

    Brian1954 Senior Member

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    I agree that replacing the battery is part of the solution. See post #8.
     
    #15 Brian1954, Sep 21, 2025 at 12:39 PM
  16. Paul Gregory

    Paul Gregory Senior Member

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    Well, based on the evidence, your opinion is weightless.
     
    #16 Paul Gregory, Sep 21, 2025 at 12:45 PM
  17. Brian1954

    Brian1954 Senior Member

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    I did not see any evidence. My opinion is just as valid as your opinion. That is why they are called opinions.

    Well, I guess you will continue using the jump starter until you sell the car and someone else fixes the problem.
     
    #17 Brian1954, Sep 21, 2025 at 12:51 PM
  18. Paul Gregory

    Paul Gregory Senior Member

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    If you are going to discount my evidence as "opinion," I can't help you.
    I doubt anyone can.
     
    #18 Paul Gregory, Sep 21, 2025 at 12:58 PM
  19. ChapmanF

    ChapmanF Senior Member

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    Heartening words to see from the member who achieved PriusChat fame by insisting a gen 5 Prime had an AGM battery, from post #66 on page 4 of a thread clear through post #150 on page 8, discounting all supplied evidence as "opinion" until finally looking at the battery for himself in #153, and by mistaking the battery state sensor assembly for a part of the battery itself, in post #42 of another thread, where four pages later in post #107 he was still rejecting all photos, wiring diagram excerpts, parts diagrams, and parts catalog entries showing otherwise, as somehow not being evidence, before the moderator locked that one.

    Maybe a moment of reflection has occurred?
     
    #19 ChapmanF, Sep 21, 2025 at 1:36 PM
  20. Paul Gregory

    Paul Gregory Senior Member

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    Maybe you are obsessed with trying to start something.
     
    #20 Paul Gregory, Sep 21, 2025 at 2:10 PM
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