Keeping track of battery degradation... after almost 2.5 years

Discussion in 'Prime Care, Maintenance and Troubleshooting' started by MSantos, Aug 14, 2020.

  1. MSantos

    MSantos EcoAccelerometry

    Oct 5, 2006
    Canada, Winnipeg
    2018 Prius Prime
    One topic that seems to come up quite often is the issue of battery degradation and how to properly track it.

    In all fairness, I cannot make the claim that I know how to properly track the degradation over time and use. However, I did start with a clean slate and my usage and driving patterns remain relatively stable if not downright boring.

    So in my case, here's my high-level usage pattern for the 2018 Prime:
    - The vehicle has been driven almost every single day since early 2018 for a total of 3.5 MWh of energy delivered to the EVSE. Energy efficiency as indicated in the Monitor 2, currently at 12.1 kWh/100km (5.1 Miles/kWh).
    - My daily commute is always under 25 miles. In the summer months, I arrive with the SoC at 50% or higher. In the colder winter months (in Winnipeg) the SoC rarely goes below 30%.
    - Except for the occasional longer trip out of the city, the vehicle is driven 99.9% of the time in EV all year round.
    - The vehicle is always plugged in and charged on arrival to the garage. May undergo multiple battery tops offs in one day.

    To summarize, I would say I make frequent use EV, I charge often, and never completely deplete the battery pack. So far, I do not notice any degradation going by driving and usage experience alone.

    Now since the devil is always in the details lets have a look at the latest snapshot of the battery pack. I perform a snapshot every 6 months just to see how the balance between the modules is kept. The snapshot is performed with HVCheck over a 24-minute driving session, on a fixed driving path (preferably on Sunday mornings... due to low traffic on the streets).

    So far, I can see 9 blocks that are beginning to stand out with an average delta over 0.01V (Stats as of August 2020):

    After looking at the block details, it appears block 58 (already with a delta of 0.02V) along with the next 8 blocks (likely already over 0.01V) are showing the greatest deviations.

    The following is a snapshot captured 2 years earlier:
    So what does all of this mean?

    Unless someone can suggest an alternate narrative, it appears the degradation is measurable through instrumentation even though it is not noticeable in everyday usage.

    While a change of just 0.01V is hardly something to write home about, I am somewhat curious to see what are other Prime owners seeing in their cars?

    Also, I am wondering if it makes sense to have a community repository that we can all contribute HV Check data to?

    Still, I remain skeptical of the reports and allegations of higher than industry average battery degradation in Prime. If these claims are true, then it must be a phenomenon of climates and usage patterns way more severe than mine.

    Thoughts, suggestions, criticisms?

    NOTE: The HV Check (battery test) was performed with Hybrid Assistant over a 15 km course (a little over 9 miles). Tire pressures were monitored with Tire Assistant at 37 PSI on all 4 corners.

    #1 MSantos, Aug 14, 2020
    Last edited: Aug 14, 2020
  2. bisco

    bisco cookie crumbler

    May 11, 2005
    2012 Prius Plug-in
    Plug-in Base
    nice tracking and write up, thank you. i agree, most owners with more degradation are probably in warmer climes
    Michael Wood likes this.