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2.75% degradation after 30k miles

Discussion in 'Model S: Battery & Charging' started by David99, Dec 11, 2014.

  1. David99

    David99 Active Member

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    As I wrote many times, using the rated range as a method to determine battery degradation is not an accurate way, IMHO. The standard method to measure battery capacity is to fully charge it, then fully discharge it (within healthy limits).

    When my 85 was new I did exactly that on a long trip. I charged 100% and drove it to 0 and got 76.6 kWh out of it.

    9 months and 30k miles later I did a similar trip. I was able to get 74.5 kWh out.

    That's a difference of 2.75%. In other words I lost 2.75% battery capacity. Now both trips were not identical, the temperature was roughly 20 degree warmer back then when it was new. Since the battery capacity and performance is actually slightly better when it's warmer the actual loss of capacity might be less. The second trip also included a 2 hour stop without charging, so there was a little bit of vampire loss which the car does not include in the energy usage display. So maybe another 0.1-0.2 kWh more. So the 2.75% is definitely on the far side.

    A capacity loss between 2% and 3% after 30k miles isn't too bad. If capacity loss was a linear curve, it would be 6-9% per 100k miles. 12-18% after 200k miles. Again that is if it was a linear curve. Only time will tell if it's linear or not. Many people claim degradation starts faster and then flattens out, but I have yet to see evidence/data that shows it.

    I very rarely charge higher than 90%. Mostly I charge between 70-90% over night and then don't charge at all during the day and drive an average of 100 miles a day. 30% of my miles were driven on long trips using Superchargers. Living in Los Angeles, the average temperature here in the last 9 months has been rather hot. Maybe not like Arizona, but close.
     
  2. walla2

    walla2 Member

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    Nice numbers. It shows that some packs do quite well. My refurb pack on its last charge only had 66.8 kwh in it. That's a 13% decline at 10,500 miles. More than 1% per thousand. My pack had your rate of deterioration until it was replaced with this refurb pack.

    It's good to have numbers in terms of kWh since rated range seems to be a moving target. Anyone else have kWh numbers? I've seen some here but only a few report what a range to low miles shows.
     
  3. Txy

    Txy Member

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    Wow, that seems abormally bad, doesn't it? Have you tried to balance the pack recently? That kind of degration after only 10k miles... ouch.
     
  4. scaesare

    scaesare Active Member

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    Mind sharing what you specific charging regimen is?
     
  5. walla2

    walla2 Member

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    I charge 90%. That worked great on my original with minimal loss at 13 months until the clunk. This charge style stabilized my range drop, but this refurb just dropped on delivery of the car back from service. I lost over 12 miles rated at 90%. I've been told it's a calculation error to be fixed by but not entirely convinced.

    BuT I'm more interested in:

    Pack A - refurb or not - 10.5 k mIles - 66.8
     
  6. Zextraterrestrial

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    #6 Zextraterrestrial, Dec 12, 2014
    Last edited: Dec 12, 2014
    this is all I can provide
    but this is power in.

    79kWhr added 6-261mi rated @ 55F A pack 3800 mi

    70kWhr added 0-236 (90%) @ 44F B pack, new
    75kWhr added 5-258mi rated @ 72F B pack 3k mi (not 100% - 100%=265)
    75kWhr added charging from 9-261mi rated @ 68F B pack 10k miles


    most used was on my A pack
    75.9 kWhr 265-0mi
    and charging back to 92% took 74kWhr
     
  7. ThosEM

    ThosEM Space Weatherman

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    I was very suspicious of the rated range, also, but I'm starting to buy into it, if only because it is such a hassle to verify it with a full discharge. Not to mention that full discharge is not considered to be good for the battery. I did "scaled" discharge assessments and concluded that I have about 75 kWh of capacity above zero range for my MS, consistent with other assessments.

    I was leery of full range charges for a long time, and the first one I ever did carefully came out at 416 km (vs a nominal 424 km, or 265 mi advertised) at 15000 km on the car. About six months later, at 30000 km on the car, I am getting 412 km on a range charge, down by only 1%, but down by 3% from the original claimed range.

    FWIW...
     
  8. David99

    David99 Active Member

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    You don't have to go all the way to zero. You can stop at 10 or 20 km/miles and add that to the energy usage. Towards the end, the range estimate is pretty accurate (according to an email from Tesla) and the margin of error is very small. If you have 12 miles left, multiply it by 0.3 and you have the remaining capacity in kWh. Add that to the trip meter energy usage and you have a pretty good number.
     
  9. mknox

    mknox Well-Known Member

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    I'm down about 8% at 40,000 miles or so. I asked Service to investigate and advise when it was in earlier this week to see if this would be considered "normal" or not. I have to go back for a follow-up visit (huge snowstorm prevented road-testing for a separate issue I reported) so have not heard back yet. For me, it's more of a curiosity than a complaint only because I talk to many others and see threads like this which seem to imply my results are worse than average.
     
  10. Doug_G

    Doug_G Lead Moderator

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    Remember that the range is an estimate, and it's actually quite hard to estimate charge state with Li-Ion batteries because of their nearly flat voltage characteristic during discharge. The voltage doesn't drop very much until the battery is nearly exhausted. As a result Tesla uses an algorithm that measures the amount of charge going in and out to help with its estimates, backed up by voltage measurements, so if you always stay in the flat region it can get off a bit.

    If you want the most accurate range estimate you need to charge to 100% then drive it down as low as you dare. That way the car "sees" 100% charge and nearly 0% charge. Then it can recalibrate its range estimates
     
  11. mknox

    mknox Well-Known Member

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    One of the things I've found curious about this is that folks who have had a main battery pack replaced report instantaneous improvements in the range estimates as soon as they get their cars back with the new or refurbished batteries. @islandbayy has reported quite a bit on this in a couple of other threads. This suggests to me that either the "smarts" for doing the range calculations must be embedded into the battery pack or there is some real degradation going on. The only other explanation would be that Tesla is re-setting something when the packs are replaced. Why I doubt that is because it seems to me that Tesla would simply do this "reset" for other owners who have been questioning their range drops.

    When I got my car back from Service last Thursday after having questioned it, they had it charged to 100% (reporting 246 miles / 396 km). I am jumping the gun here because I do have to bring the car back and have not yet heard what they've had to say about it.
     

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