Tesla Model S Battery Degradation

Discussion in 'General' started by Carcus, Apr 4, 2017.

  1. Carcus

    Carcus Well-Known Member

    Just a couple of small and not too useful data points, ....

    Pulling data from the 5 oldest cars from a the Asia, Pacific & Europe, excluding UK, I found:

    Avg battery age: 1185 days, 3.24 yrs
    Avg batter cap: 92.28%*
    Avg miles driven: 87,000 or about 27,000/yr

    That would have the batteries degrading at 2.4%/year. If they're good to 70%, then they'll last 12.5 years and on these heavily driven cars, 335,000 miles. But that's if degradation is linear. If the degradation "slope" starts dropping off at 85% or 80% , then that could mean a life expectancy of something closer to 8 years. And what about those users who drive a more average 15,000 miles/yr (instead of 27,000) ...?

    I guess only time will tell

    /* -- big asterisk here, this is actually percentage remaining of original range, which is not percentage of original usable capacity, which is not percentage of original capacity --- which is what we'd really want to know. Tesla keeps a lot of this hidden, .. so you just kind of have to go with what info you have.

    Last edited: Apr 4, 2017
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  2. BillLin

    BillLin MASS: 2018 Bolt EV and 2017 Prime

    You're sure those were US Miles and not kilometers, right? I can't get to the file right now, but thanks for posting.
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  3. Carcus

    Carcus Well-Known Member

    Yes. Mileage in km was converted to miles. Those guys (at least those oldest 5) must be long range commuters (i.e. 50+ miles each way would be my guess). I think it's really safer, in a way, for high mileage (and high income) users to plunge off into unknown BEV territory. There's at least some (unknown) protection via Tesla's vague "8 year infinite mile" warranty.
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  4. Carcus

    Carcus Well-Known Member

    Last edited: Apr 5, 2017
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  5. Carcus

    Carcus Well-Known Member

    Some more guessing,

    After looking at the data for a while, (not scientific, I know) , there looks to be some correlation between low miles and less wear on the battery -- but there is not a strong correlation. It looks like age is at least as important, and likely more important, than miles. I wonder if this might be because the low mile cars may still be getting similar heat cycles (but not kwh cycles), .. thus the battery still ages at roughly the same rate as high mile cars.

    It might be the ranking of factors with degradation are
    1. Age (while being used to some degree, not to be confused with careful storage)
    2. Heat (heat cycles, and time spent at elevated heat)
    3. Cycles (miles)

    this would be different from a lot of the on-line info I see, where the focus is almost exclusively on cycles. I have seen the (Tesla associated) battery guru video, and he talks a lot about heat. He has also said (more than once) that we are currently at "10 year" batteries.

    Many will say, "well, the Tesla has a great cooling system, so that takes care of that". Obviously, that's a big deal but..when you think about the heat is being generated down in the core of each cell (I presume) there is only so much you can do to draw it out.
    -- a heat soaked pack leaving the mall in Arizona will have a totally different experience than a cold soaked pack leaving a ski resort in Norway.
    -- and now that they're towing with the Model X (and soon will be with the Model 3?) I would think with a high drag load and 70 mph, (and stopping every 100 miles for supercharging (also adding heat) will put some noticeable wear on the pack.
    Last edited: Jun 20, 2017
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  6. Carcus

    Carcus Well-Known Member

    And a few more thoughts,...

    Tesla power walls are warrantied for 10 years. Normal degradation is not covered.

    I spent some time looking at the roadster forums and searching for clues. I, personally, could not find any evidence to point to a battery that will exceed 10 years,... I found one that went normal usage (about 14,500/yr) 7 1/2 years. Again, no hard evidence.. just internet creeping. Maybe Tesla's new cell in the 3 will have some secret sauce, ... and maybe it won't.
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  7. SageBrush

    SageBrush Active Member

    I've seen more data over at teslamotorclub.com but I cannot remember details beyond the degradation being modest. In general it seems to be true that the first year has the most percentage loss and by year #3 the rate is low. If that trend continues then the entire story of battery degradation will fade into the background for Tesla.
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  8. Jay

    Jay Well-Known Member

    It's hard to make a generalization from a few cases when we don't know all the particulars.
    1. Heat is the main enemy of battery life. So what conditions were they driving in?
    2. Heat is the main enemy of battery life. So how many "fast" level 3 charges vs slower charges on the packs?
    3. Heat is the main enemy of battery life. High miles at speed will heat the battery packs more than slower miles. High speeds in hot conditions and then adding a level3 charge is very hard duty for the batteries.
    4. Keeping the batteries between 40% and 70% charged will greatly extend battery life. How often and how long did they operate outside those parameters?

    I remember hot desert climate Leaf owners successfully sued Nissan for excessive and early battery degradation. Many owners would fully charge their batteries and leave the batteries at full charge overnight before heading off into the scorching hot day. The litigators argued that they weren't told that these conditions would waste their batteries.
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  9. Carcus

    Carcus Well-Known Member

    Last edited: Jun 20, 2017
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