1. Attachments are working again! Check out this thread for more details and to report any other bugs.

2021 Prius Prime traction battery: the first year degradation

Discussion in 'Prime Technical Discussion' started by Salamander_King, Sep 6, 2022.

  1. Salamander_King

    Salamander_King Senior Member

    Joined:
    Nov 8, 2015
    10,963
    8,839
    0
    Location:
    New England
    Vehicle:
    Other Hybrid
    Model:
    N/A
    Here is the first analysis of the traction battery degradation on my 2021 PP. I now have owned the current PP (2021 Ltd) for 14 months. This is my third PP. On this car, I have kept a daily record of kWh used to charge the traction battery for each charge session using a kill-a-watt meter on L1 EVSE. For each charge session, the % SoC charged was also recorded to extrapolate the kWh used for the "full charge" for the session. Using those data, I calculated the monthly average for the kWh used for a "full charge" (0 to 100% on the dash).

    Below is the summary of monthly average data with the sample numbers and standard deviation. Plotting the value with SD for the error bar, I can clearly see the decreasing trend. Of note, one month (Dec) value 7.22kWh is higher than any other month with a large SD. This is because the traction battery had the "battery heater" on. For the following months, this "battery heater" function was turned off. No "battery cooler" function was used. Also, "Climate Preconditoing" was never used.

    Comparing the Aug 2021 average of 6.71kWh+/- 0.16 and a year later Aug 2022 average of 6.41kWh+/-0.12, the difference is statistically significant (i.e. the error bars do not overlap). Accordingly, the rate of traction battery degradation calculated is ~4.5%/yr.

    upload_2022-9-6_15-3-51.png

    I don't know how this rate will change after the first year. I have anecdotal evidence to support the idea that the degradation is more pronounced in the first year and somewhat stabilizes after a few years. Here is the graph of similar data taken from my other two PPs. 2017 PP was kept for 30 months, and 2020 PP was kept for only 10 months. The 2020 PP (Red bars) shows a very similar rate for the decreasing kWh for a full charge for the first 10 months as the 2021 PP (Green bars). Unfortunately, I did not keep the record for the 2017 PP (Blue bars) between months 5-16. But after 24 months, the 2017 PP full charge kWh number is similar to 12 mo old 2021 PP data.
    upload_2022-9-6_15-29-18.png
     
    #1 Salamander_King, Sep 6, 2022
    Last edited: Sep 6, 2022
    MTN, drash and Downrange like this.
  2. schja01

    schja01 One of very few in Chicagoland

    Joined:
    Apr 22, 2005
    1,732
    1,156
    0
    Location:
    Chicagoland
    Vehicle:
    2018 Prius
    Model:
    Prime Advanced
    What kind of miles per year?
     
    Salamander_King likes this.
  3. Downrange

    Downrange Active Member

    Joined:
    Apr 15, 2010
    352
    179
    2
    Location:
    Canada
    Vehicle:
    2024 Prius Prime
    Model:
    SE
    Excellent post, thanks for the data! Six months and 10k miles into my 2022, and still loving it! Hope to get 10 years and 200k from it!
     
    Salamander_King likes this.
  4. Salamander_King

    Salamander_King Senior Member

    Joined:
    Nov 8, 2015
    10,963
    8,839
    0
    Location:
    New England
    Vehicle:
    Other Hybrid
    Model:
    N/A
    On current 2021 PP, ~10K miles in 14 months with an average of 2-3 charging sessions/week but not always 0 to 100%. On 2020 PP, I only drove ~3,600miles in 10 months and did very little charging maybe once a month. On 2017 PP, I put ~40K miles in 30 months with a daily full charge almost every night.
     
    #4 Salamander_King, Sep 6, 2022
    Last edited: Sep 6, 2022
  5. prius16

    prius16 Active Member

    Joined:
    Nov 3, 2015
    462
    241
    1
    Location:
    New England
    Vehicle:
    2022 Prius Prime
    Model:
    Limited
    Good Informataion!


    Where did you get the State Of Charge?
    The displayed SOC displayed by the car/app is so-so.
    So, far, I've noticed, a max difference of ~4% between the actual SOC, and the displayed SOC.
    Btw, the actual and displayed percentages, are obviously not 1-to-1.
    Iirc, ~84% actual = 100% display. ?~15%? actual = 00% display.
    You need Hybrid Assistant, or a capable scanner to read the actual SOC.

    Another note, being in New England, charging at 240V, and charging at night, the "Turn On AC function" may not be needed.
    Also, if the car is in an attached garage, then the battery heater function may not be needed

    Iirc, the AC and Heater can both use up to ~~2kWatts.
    Iirc, I've seen ~2.1kW and 1.9kW (heat/ac) observed on my scan tool, at some random Summer New England nights around 8pm.
    Iirc, the lights use ~0.6kW to 0.9kW (always low beam, no long traffic lights), based on back to back later-time drives using cruise control on similar weather & traffic days.

    Fwiw, I use the Hybrid Assistant app (pretty much on every drive), and I set the battery fan for a max battery temp of 35C.


    I mentioned in another thread, that I tried the Dr Prius Battery Life Expectancy Test on my Gen4 Prius Prime. I couldn't get it, or figure out, how to get it to work on a Gen4 Prius Prime. It's not clear anywhere, that the battery life test even works on a Prime or PiP.
    It seems like a great an useful app.



    Thanks again for the Great information!
    (y)
     
    Salamander_King likes this.
  6. Salamander_King

    Salamander_King Senior Member

    Joined:
    Nov 8, 2015
    10,963
    8,839
    0
    Location:
    New England
    Vehicle:
    Other Hybrid
    Model:
    N/A
    For this analysis, I used SoC displayed on the dash for all of the data points. The absolute value of SoC level in the traction battery is not important for this analysis, as long as consistently using the same L1 EVSE connected to the same outlet and reading the SoC off from the dash, the comparison from 1 year ago to now is valid. You are correct that the traction battery heater, traction battery cooler, and also climate preconditioning all use the wall kWh while the car is being charged. That's why I turned off the traction battery heater after seeing a big spike in the monthly average in Dec. Using any of those three functions will make the comparison very difficult.

    As far as the comparison of the SoC displayed on the dash MID vs the SoC reported by HA, here is the copy of my comment from another thread edited for this tread content:

    The MID SoC level and the absolute SoC level (reported by Hybrid Assistant) are perfectly linear relationships between MID 0-100% corresponding to HA 14-84%. Using the colinear points to generate a graph shown below (x) is the value of SoC reported by HA and (y) is the SoC displayed on the dash MID.

    This linear function can be written as

    y=(100/70)x-20

    So, the dash SoC is off from the absolute SoC, but since it is perfectly linear, it makes no difference in the analysis of the full charge which is always 70% of the absolute SoC.

    [​IMG]

    Screenshot_20220902-061014.png
     
    #6 Salamander_King, Sep 6, 2022
    Last edited: Sep 6, 2022
    Rocketboy235 likes this.