Dr. Prius says pack capacity increased 3%, noise?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by pasadena_commut, Oct 26, 2023.

  1. pasadena_commut

    pasadena_commut Senior Member

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    The pack on our 2007 (the original) seems to have problems with sustained loads when the motor is off, like sitting with the A/C running, or driving slowly with the lights on. Under those conditions the SOC can drop very rapidly from green all the way down to purple. (Sometimes it sits at purple for a while without the engine starting, leaving me wondering what it is waiting for.) Once the car is moving again SOC goes back up pretty fast, but not as fast as it falls. Seems like the pack has low capacity, but it doesn't throw any codes. MPG is still 49ish with mostly highway driving, and maybe a hair lower for suburban driving than when we first got it used. But when it was newer the SOC didn't collapse like that.

    In January the "life expectancy test" said 51%. Tested it again a few days ago and it said 54%. (Unfortunately, hit the wrong button on the most recent test and didn't save it.) Does it even make sense for a pack to recover capacity all by itself, or is this just an indication of the noise level in the measurement?

    The resistance had risen slightly from 26-27 milliOhms to 27-28 milliOhms with one at 29. The voltage differences are still small.

    Dr. Prius has added another bar graph between the module voltages and module resistances "cumulative delta voltages". What is it and what should the values be?

    There is a video here:



    but it doesn't say what a good value is and what a bad value is. I think he said that it is just the difference between the highest and lowest voltages for the length of the measurement, but that isn't "cumulative" (implying some sort of integration over time), it is "maximum delta voltage".
     
    #1 pasadena_commut, Oct 26, 2023
  2. Tombukt2

    Tombukt2 Senior Member

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    Yes your battery is getting old your battery HD battery has not much to do with your lights driving around slowly either when the battery is going bad the engine will come on quite a bit to take up for that magenta looking bars you have to bring them back to blue and try to head them towards green which you will see magenta blue to green very quickly way quicker than you've ever seen before in your life this is a sign that the battery is going down the tubes your battery is also an '07 so what's that now 17 years old or something most of these batteries generally last the life of about 10-12 maybe so you're going to be the guy that goes for 20 years I guess sounds good as long as you're close to home and you're not spending a lot of money on towing the car around playing these games well I guess have at it I've seen a car with $435,000 mi on the original battery and it was still driving reasonably okay and this person has never done anything to the battery and I mean nothing no charging no discharging no any funny business I would be getting on changing that battery very quickly these folks don't seem to be too worried about it of course this is Mama's secondary car and they all have newer cars just in case so if you're set up like that and you have backups then no worries that's why I have like five of these things so it never puts any pressure for me to worry about any car nonsense because we have plenty they're almost free these days.
     
    #2 Tombukt2, Oct 26, 2023
  3. mr_guy_mann

    mr_guy_mann Senior Member

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    You're dealing with "noise". There are a bunch of variables involved with a "guestimate" test of battery capacity.

    I would monitor block voltages when SOC drops and rises quickly. And probably be filling my piggy bank towards battery replacement.

    Posted via the PriusChat mobile app.
     
    #3 mr_guy_mann, Oct 26, 2023
  4. PriusCamper

    PriusCamper Senior Member

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    Old NiMH batteries need deep cycling to restore capacity: BU-807: How to Restore Nickel-based Batteries - Battery University

    Also Gen2 is susceptible to corrosion caused by leaky seals at the terminals and once that corrosion gets inside the battery ECU you'll start to get sudden drops in voltage that return to normal in a matter of minutes. Once it progresses, it shorts out the ECU.
     
    #4 PriusCamper, Oct 26, 2023
  5. pasadena_commut

    pasadena_commut Senior Member

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    Does the pack have to come apart to check for that corrosion, or is it maybe visible after removing the orange plug and looking in through the hole? (With a mirror or scope I guess, no space for a head to peek in directly.) Otherwise it is 7 minutes into this video:



    before the ECU is exposed.

    What is the part number for the 3 white clips that attach the top of the pack to the panel which is part of the hatch floor? When I cleaned the fan last time those didn't fare too well and they should be replaced if I ever pull that panel off again.
     
    #5 pasadena_commut, Oct 26, 2023
  6. PriusCamper

    PriusCamper Senior Member

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    They're just standard Toyota interior fasteners...

    And yes you can pull the ECU and look inside and clean it without pulling the pack, which will buy you some time but won't clean up the source of the corrosion.
     
    #6 PriusCamper, Oct 26, 2023
  7. pasadena_commut

    pasadena_commut Senior Member

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    "Standard" doesn't really apply to the world of car fasteners. They look something like these, but I'm not sure the size is right:

    https://www.fastener.zone/collections/toyota-fasteners-and-clips/products/auveco-18876-3262-toyota-90467-a0006

    So no, looking through the safety switch hole won't do, the case has to open to access the ECU.
     
    #7 pasadena_commut, Oct 26, 2023
  8. dolj

    dolj Senior Member

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    #8 dolj, Oct 26, 2023
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