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Questions about Dr Prius Life Expectancy Test

Discussion in 'Gen 2 Prius Main Forum' started by davecook89t, Aug 28, 2019.

  1. davecook89t

    davecook89t Senior Member

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    So with 12+ years and 277K+ miles on our Gen 2, I know our HV battery is on borrowed time. Therefore, we have been sticking fairly close to home with the car the past few months. Now however, we are planning a trip out of town of 100 miles or so this coming weekend. Seeking some assurance it would be not a huge risk to take this car, I decided to run a Dr. Prius Life Expectancy Test on the battery. On the discharge portion of the test, I started out holding the car in reverse, with the AC on full blast and headlights on as instructed, but was not comfortable with the back-up camera preventing the MFD's state of charge from being displayed, so I switched from Reverse to Neutral, so I could watch the number of bars. The charge portion of the test had ended with all 8 bars showing on the display (which I was also slightly concerned about, not being sure that the battery could not be overcharged by force-charging it to that level). Anyway, I found I was able to keep the needle in the green portion of the range during the discharge test, even with the car in Neutral rather than Reverse, and the number of bars was still holding at 7 and then 6, several minutes into the cycle. About half-way through the projected discharge time, however, the remaining bars began to disappear rather quickly. Finally, the display got down to the last bar and the estimated time to complete the test was still about 5 minutes, so at that point I chickened out and baled, putting the car back into Park.

    So, first question. Was the app really going to require that I drain my battery to the point where recovery was not assured just to complete the test, or would it have instructed me to abort before the remaining 5 minutes had expired?

    Next question. The app did give me a life remaining estimate of 56%, although it came along with a warning that the test did not complete. Does that mean anything or should it be totally disregarded?
     
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  2. 2k1Toaster

    2k1Toaster Brand New Prius Batteries

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    The tests are pretty useless. They are good intentioned but the sensors just aren't capable of that kind of resolution to get 56%.

    Also you didn't have a high draw on the battery (not in R) so it is even more useless.

    And you don't seem to understand the battery in the Prius in the first place.

    You
    can never harm the battery in the Prius when there are no codes shown and you have it READY in D/R/B/P.

    When the battery shows 8/8 bars, it is near 80% SOC. The car will actively try to reduce the battery charge by spinning the engine without fuel to waste energy. Just like you cannot put more energy into it. The HV controller won't allow it. Even with regen braking or force charging it won't happen. Similarly when the battery bars are at 1/8 bars you are at around 40% capacity. The car will not allow you to draw any more power from the pack, and will spin the engine up to charge the battery.

    Look at one of the exceptions to my above statements, when in N you can kill the car. When it gets to 40% the car will not allow the engine to spin up, you're in neutral. Eventually this will drain so far that you cannot start the car. This is somewhere in the sub-10% range. The other way to do this is to run the car out of fuel and then keep going. And then turn it on and off multiple times without adding fuel.
     
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  3. davecook89t

    davecook89t Senior Member

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    Isn't it true that the ICE cannot charge the HV battery in R as well as N?

    Right, that's why I aborted the test. How do I know whether or not Dr Prius would have instructed me to stop the test before the battery was completely dead? I guess I just didn't trust that the app had enough battery protection programmed into it.
     
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  4. davecook89t

    davecook89t Senior Member

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    Even in Neutral, I was able to keep the needle in the green area of the gauge, which is supposed to represent the recommended draw rate. Even in Neutral, at one point Dr. Prius gave a message that the draw was too high, so I raised the temperature setting on the AC a few degrees to get more towards the middle of the range.
     
  5. PriusCamper

    PriusCamper Senior Member

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    One of these days we need to meet up with Dr. Prius dude and work through his test with battery packs that have solid spread sheets of data to test for accuracy... But in general, like yourself, it's tempting to give up on it.

    Keep in mind too that the charge bars on your screen is not like your fuel gauge... Your fuel gauge gives you 10 squares to represent the whole tank and you can drain it all the way down to one square flashing and have a near empty tank. Whereas your battery charge give you charge bars that is the roughly equivalent of seeing only 5 to 9 squares on your fuel tank gauge because Toyota designed the system to not run on max charge or at a super low charge. Point being when you're down to one bar of charge on the screen you still have quite a bit of battery charge still in the pack, so no worries there.

    As for your 100 mile road trip, you'll be fine... The reason some Taxi cabs have gone 500K miles without a hybrid battery failure is because the battery is always in use, always charging and discharging, which keeps the pack healthy. What's hard on a battery pack is when people who live on top of a hill drain the battery down getting home and the let it sit for days at home with a low charge. Also hard for a pack is parking the car in a parking lot with the windows rolled up on a super hot day which makes the interior and the battery super hot and then go sit in traffic and all the heat and discharging could lead to failure. On your road trip use the Prius App to monitor hybrid battery temperature. While it's normal for the pack to get up above 100' during portions of a long drive, if you're going to have a failure while driving, it's most likely only going to happen when the temps get way up over 100 degrees, so avoid all that as best you can.

    Lastly, if you put in a brand new battery pack, what you'll see that will be different on your screen is the amount of charge bars won't fluctuate very much at all. This is because an NiMH battery packs lose capacity over time and Toyota designed their packs to functional normally even at only 50% capacity (sudden full charge and rapid discharge on your screen).

    And in the same way you deep cycle rechargeable batteries to condition them, you can do this with your pack using some lightbulbs to discharge and then a high voltage trickle charger to charge and balance. Once you do this several times you can restore capacity of the pack up to 96% of brand new and if you keep doing it a couple-few times a year you can get more years of life out of your pack without have to buy a rebuilt of brand new one. Learn more about all this here: FAQ
     
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  6. Skibob

    Skibob Senior Member

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    In my 2006 Prius if I’m in reverse and I hit the Info button on the steering wheel it turns off the backup camera and goes back to the energy monitor screen.
     
  7. davecook89t

    davecook89t Senior Member

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    Good info, I'll keep that in mind if I ever decide to do the test again. Thanks.
     
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  8. C Wagner

    C Wagner Member

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    Bit of an old thread here, but wanted to add my Dr Prius Battery LIfe Expectancy test results.

    The back story was that the car was bought with a bad HV battery, I know because when I test drove it the Red Triangle Of Death came on, and 4 modules tested around 6x by me on the workbench and would not reincarnate, no matter how much slow cooking/discharging I did. After replacing those with used tested good-voltage modules, and cycle charging all modules followed by a 24 hour balance, I put the HV back in the car.

    So, my result (with a couple minor 'outside the green' band warnings, quickly remedied) was 102% - your battery is new. This result was a relief, but made me question the accuracy of the test. Does 102 definitely imply not 50%? I hope so.

    I suppose I'll retest in moderate weather with an even more intense attention to keeping the amp meter arrow in the green than I thought I was doing the first time. I note that large amp draws you can play with are: rear defroster (on/off), headlights (can go down to parking, turn on fog lights), air conditioner (can make it colder warmer) and reverse with parking brake firmly applied. For most of my test, Dr Prius had me staying in P on its instructions and fiddling with AC, headlights, rear defroster.
     
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