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Tesla's 85 kWh rating needs an asterisk (up to 81 kWh, with up to ~77 kWh usable)

Discussion in 'Model S: Battery & Charging' started by wk057, Feb 2, 2016.

  1. wk057

    wk057 Senior Tinkerer

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    #1 wk057, Feb 2, 2016
    Last edited: Feb 11, 2016
    NOTE / PLEASE READ FIRST:
    2016-02-11: Just adding an important note pointing out that there is a LOT of misinformation getting thrown around and perpetuated in the replies here on this thread. I have no control over what other people post/reply, and I can't waste time battling random people on the Internet every time someone posts something that's completely false, misleading, or otherwise twists the facts into something they're not. I've posted the data that I can and my conclusions based on the data I have collected. I hope, among other things, my reputation here speaks for itself when you come across replies here with outrageous claims, unsubstantiated claims of knowledge of Tesla's inner workings, and other attempts to discredit me or my findings. I'm always fine with someone presenting data that opposes my own, but no one here has done so (nor in my opinion is really able to legitimately do so given that the data pretty much speaks for itself).

    In an effort to spare my sanity and make much better use of my limited free time I'm unsubscribed from this thread and will not be following up on this matter further. Keep an eye out for more fun projects. :)

    --- (Original Post) ---

    Alright, so this discussion has been going on in other threads and I keep chiming in with bits and pieces of details. I guess it's time to make the sure to be heated thread. Please read this entire post before commenting. It's likely I've answered your question or countered an argument you'll make already. I already know I'm going to catch hell for this one.

    As many of you know, I'm pretty much the local self-proclaimed expert on Tesla's batteries. I'm using 15,984 cells from Tesla battery packs to power my house with my off-grid solar setup. I've disassembled two full Tesla battery packs, assisted with the disassembly of another's, and have disassembled a couple of modules into individual cells for various torture tests. I've also acquired roughly a dozen cells from a "60" pack with < 2500 miles to compare to my "85" pack cells.

    I presently have had roughly 20 pairs of cells from Tesla's "85" kWh pack running 24/7 doing various cycle tests in various conditions. (Eventually I'll be posting detailed data from these tests, but I want to give them significant run times.) These cells were from a pack that had less than 1000 miles (or less than 5 charge cycles) on it, and arrived to me charged to roughly 50% (perfect for storage/shipment).

    I've also done capacity testing on full modules.

    More recently I have been investigating other aspects of the Model S via my bench setup. Many details on that in my other thread, but here I'll focus on battery related items.

    I'll point out that I have no first hand or otherwise verifiable data on the 70 or 90 packs thus far.

    Let's run through some quick facts.


    • Tesla's "85" kWh pack consists of 16 modules of 444 cells for 7,104 total cells.
    • Tesla's "60" kWh pack consists of 14 modules of 384 cells for 5,376 total cells.

    Now, right away there is a problem and we haven't even gotten to any testing or other data yet. If 7104 cells total 85,000 Wh, then each cell would contain 11.965 Wh of energy. If 5376 cells total 60,000 Wh, then each cell would contain 11.161 Wh of energy. Hmmmm. These numbers don't add up. No big deal, maybe they used different cells in the "60" pack you might argue. Now for some test results.


    • Individual cell testing of capacities of the cells from the "85" pack and the "60" pack match to within 0.5%.

    OK, so, they've definitely the same exact cells. How can Tesla possibly be rating one pack as 60 and one pack as 85 then knowing the above? And we haven't even gotten very far here yet and this is already a red flag.

    Now, OK, let's actually test these cells and see what happens. There has to be a real number. Turns out the cells are very consistent in capacity testing. VERY consistent.

    In 6 hour charge/discharge cycle testing (1/6C charge and discharge) over a one month period the average capacity of the cells came out to 11.36 Wh per cell. The maximum capacity measured was 11.42 Wh/cell.

    Extrapolate this out: 7104 * 11.36 = 80,701 Wh (80.7 kWh) for the "85" pack cell count, and 5376 * 11.36 = 61,071 Wh (~61.1 kWh) for the "60" pack. This means the "85" rating is short by at least 5%, and the "60" rating is under-rated by at least 2%.

    Sounds small, but here's some more data.

    This means that the "85" pack is "missing" about 4.3 kWh of capacity. That's about 14 miles of range.

    "Oh, but it's a buffer... the anti-brick thing, wk!"

    Glad you brought that up. Since I did my cell testing outside of the Tesla BMS and anti-brick stuff, I was able to discharge them well beyond what Tesla's setup would normally allow. So, no anti-brick buffer screwing with my tests.

    Further, data gathered from my hacking efforts revealed that the the anti-brick buffer on the 85 pack is a static 4.00kWh (NO! THIS IS NOT USABLE CAPACITY BELOW 0 MILES). So that comes out to about ~77 kWh usable, max, on a brand new Model S with an "85" pack. Hmm... oddly matches pretty much everything we've ever seen. Applying to the "60" pack gives us about 57 kWh usable, although I believe the anti-brick buffer is slightly different on the 60 pack (unconfirmed). The car's BMS also reports the usable capacity as around 76.5 kWh with a 4 kWh buffer on my own car. See my CAN deciphering document for my CAN deciphering document which includes how to decode this data. The fact that the car reports these values that match perfectly (within 1%) of my cell testing means that Tesla is well aware that these are not actually 85 kWh packs.

    So I can kind of see where the 60 number came from. It's 61, round down to an even 60. OK, good enough. But why "85"? This is not an 85 kWh pack. It's an 81 kWh pack at best, brand new, at super low discharge rates. I don't know about you, but when I went to school 81 would round to 80, not 85.

    It might not sound like a big deal, but it kind of is. Today, Tesla has a 90 kWh pack upgrade (which is likely not actually 90 kWh either, but unconfirmed) that costs $3000 for an additional 5 kWh. Well, the "85" pack is missing 4 kWh to begin with, so extrapolating that out everyone with an 85 pack overpaid by about $2,400. As the buyer of a total of three 85 version Model S, that's $7,200 worth of capacity that I never received. That's significant.

    Further, these cells are almost certainly NOT Panasonic NCR18650B cells, like many have assumed. Close, but not identical. I've tested actual Panasonic NCR18650B cells on the same equipment as the Tesla cells, and the retail Panasonic cells always perform better and have slightly lower internal-resistance. So, the NCR18650B specs are not quite relevant.

    Many people keep bringing up hard drive capacity ratings as a parallel, but that's totally different. Sure, you could say that the usable capacity is analogous to the formatted usable capacity of a hard drive... I can go with that. But here's the thing. Prior to formatting a 1TB hard drive, there are 1,000,000,000,000 bytes available to the system to use, or exactly the definition of 1TB. So, the capacity is there on the physical device. In the case of Tesla's "85" kWh pack, the initial capacity isn't there to begin with (81 kWh total from completely full to completely dead). So, the analogy falls short. Let's not try and use it anymore.

    Additionally, back to my solar project, I closely monitor the power output of my battery bank. The capacity measurement there matches my other testing and information gained from my hacking efforts to within 1%.

    Essentially, there I can find no evidence that the "85" pack is actually 85 kWh, but multiple pieces of evidence that confirm that it is not in fact 85 kWh.

    I've no idea what to really do with this info aside from share it with the community. I've already lost all faith in Tesla's published specs, personally. (See here and here for those rants...) I feel that at the very least owners of these cars and future buyers have the right to know the real specifications of the car they own or are buying.

    "Let's get it on!"
     
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  2. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    I guess it's likely a marketing thing. Is the buyer looking for a specific battery capacity? or a range?

    Most people purchase the car with the various battery packs based on range, not technical details like kWh. Buying kWh doesn't do anything for the car, while buying range is the material point of an EV. If Tesla were selling those packs for Powerwall and were short, I'd agree there's likely a material problem. But - assuming the ranges are correct - I don't know that you could consider that a material misrepresentation on the car.

    Is it the right thing to do to a primarily-techie customer base? I say 'no'. I'm guessing they were stretching for more differentiation in the model numbers. I don't like it but I understand it.
     
  3. qwk

    qwk Model S P2681

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    I suspected the NCR18650B cells are better than what Tesla has been using, but it's nice to have it confirmed. Those are some stout cells. Thanks for all of the effort, time, and hard work you put in doing these tests, and sharing them for the benefit of other enthusiasts.

    - - - Updated - - -

    Deception is deception, no matter what the reason or excuse.
     
  4. wk057

    wk057 Senior Tinkerer

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    Very sensible theory. I guess part of my issue is that if it actually were an 85 kWh pack then it would actually have more range (closer to the originally advertised pre-production ranges, or the originally advertised P85D range, etc).

    It will *definitely* be interesting to see how the PowerWall/PowerPack test out, if they ever actually start shipping any.

    In any case, it doesn't really excuse things. They could have just as well marketed it as an 80 kWh car and it'd still be fine. I don't see any other 80 kWh+ production EVs for sale. Why the need to inflate specs beyond reality? Seeing that this goes all the way back to day 1, I shouldn't be surprised by all of the P85D spec shortcomings I guess, in hindsight.
     
  5. Muzzman1

    Muzzman1 Member

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    I'm a huge tesla proponent as I'm sure you are @wk, and this thread kinda makes me sick. Like you said, they make an incredible car.
    Why didn't they just sell them as 80kw batteries??
    I wish I sold my shares a yr ago too.
    I'm bummed this will inevitably make tesla look bad in the media.
    Bummer.
     
  6. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    I don't really know why they would inflate it. Is there any outside chance that they actually had an 85 kWh target and had to trim it down after all the specs and marketing materials were announced? A 17th module that had to be scrapped? I don't really know.

    At least the ranges appear to be on target - that's the important value, IMO. Sometimes we techies need to remember the important factors in the decision-making process vs. the overly technical specifications. With the STL group, I was showing our cars (and summon!) at the St. Louis Auto Show this past weekend... only one person asked me the kWh of the battery pack - the guy from the science center that manages the EV exhibit; yet literally thousands of people asked us how far it goes on a single charge.
     
  7. Andyw2100

    Andyw2100 Well-Known Member

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    Stretching for more of a difference in the model numbers, but for what purpose? The obvious answer, but not the one many of us would want to believe is the correct one, is that Tesla wanted to make the difference in value between the higher end batteries and the smaller ones appear greater than it actually was, to encourage people to spend more money, and opt for the bigger battery. The cynical side of me thinks this is probably what happened. The rest of me hopes there is another explanation.

    As a possible alternate explanation, is it possible that Tesla had intended to use the higher capacity cells discussed elsewhere in the 85s, but then for whatever reason did not, and just made a bad decision at that point to stick with the 85 model names, instead of switching to the more accurate 80 for the model names? I know, that is probably grasping at straws, attempting not to think the worst of Tesla. This would be bad enough on its face, but not quite as bad as if the plan from the start was to deceive for the sake of deception.
     
  8. bhuwan

    bhuwan Active Member

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    I've always wished my battery have me 85 usable (and maybe the pack was actually 95)
     
  9. JohnSnowNW

    JohnSnowNW Active Member

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    O6eaHwy.jpg

    Which is how I feel about (*) in general now...thanks to this forum.
     
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  10. HankLloydRight

    HankLloydRight Fluxing

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    Tesla's 85 kWh rating needs an asterisk (up to 81 kWh, with up to ~77 kWh usa...

    Having 60 and 80 kWh packs is pretty much the same as 70 and 90 kWh packs which is the direction they're already heading (soon dropping the 85 kWh pack). They should have corrected this at the start, instead of letting the marketing dweebs have their way.

    Let's just hope the 90 kWh pack is actually 90 and not 85.
     
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  11. Andyw2100

    Andyw2100 Well-Known Member

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    34 minutes exactly. (11:16 PM time of original post, 11:50 PM time of above referenced post.)

    If you had "under an hour" in the pool, you're a winner!
     
  12. ohmman

    ohmman Maximum Plaid Member

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    It's possible that the 90 pack upgrade represents a better capacity value than is represented in the 5kWh bump, then. Making the assumptions that wk057's data is valid (I trust it) and that the 90 is really 90. But, as was mentioned above, are you buying it for the capacity or stated (and more importantly, realized) range?
     
  13. eye.surgeon

    eye.surgeon Member

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    My Ducati 1200 only displaces 1199cc. I feel like I've been robbed.

    Seriously who loses sleep over this. Most devices with batteries promote battery life, not battery size. Who here knows the exact size of the battery in their iphone or laptop? Did you know the latest iphone has a smaller battery than the previous one? Does anyone feel cheated?
     
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  14. Andyw2100

    Andyw2100 Well-Known Member

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    If you were an early adopter of the P85D, buying based on the original claims, it doesn't matter, as you apparently didn't get either.
     
  15. bh1783

    bh1783 Member

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    As long as the range and performance are as advertised it's not really a big deal. Mercedes did this with their "63" engines that were actually only 6208cc.
     
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  16. Andyw2100

    Andyw2100 Well-Known Member

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    If only...
     
  17. Camera-Cruiser

    Camera-Cruiser Fully Charged

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    So my 85 gallon tank is only 80? Yeah, I'm kinda pissed. This might only be 14 miles, but I paid for it, and I have never been thrilled with actual range vs rated.

    I had to warn my wife to watch her mileage yesterday because of the wind. She looked at me funny. So, I actually added about 15 miles before she left. So it makes a difference.

    I like my MS, but I don't think I'll buy another until they can really hit an actual 300+ miles on a normal (and that's 90%) charge driving real speeds in real weather. To me they have made the car worse since 7.0.
     
  18. ohmman

    ohmman Maximum Plaid Member

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    I served that up for you, Andy. Thank me later. :wink:

    In all seriousness, I think it's a valid point to bring up. And I don't think anyone's losing sleep over it. It's worth bringing to Tesla's attention and giving them the chance to refute or confirm it and explain themselves. There may be a perfectly good explanation. Or it may be a marketing term. My only complaint about that isn't the badging or naming - it's the fact that they list it in the specifications page on the Tesla website. If it didn't make that page, I could excuse it as being marketing badging.

    Again, I'm not losing sleep over it. I'd still buy my 85 over the 60 I could have gotten. I'm glad I have it, etc. But I don't think it's fair to completely dismiss the observation.
     
  19. commasign

    commasign Active Member

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    Another informative post. Thank you. I don't feel mislead since I bought the car with an expectation that it can achieve EPA rated miles under the stated conditions (and mine does). But I agree it's inaccurate for Tesla to call it an 85kwh pack.
     
  20. MP3Mike

    MP3Mike Active Member

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    Maybe someone was confused and thought that the 81kWh was after the 44kWh anti-brick buffer. (81+4=85)

    And it got far enough along that they decided that they couldn't back-track to 80kWh...
     
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