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Tear down of 85 kWh Tesla battery pack shows it could actually only be a 81 kWh pack [Updated]

tesla battery tear down

Tesla Model S owner and battery tinkerer Jason Hughes published this week some of his findings following his tear down of several Tesla battery packs. Hughes is best known among the Tesla community for salvaging two Tesla Model S battery packs in order to create a massive energy storage system for his off-grid residential solar installation even before Tesla introduced its own line of stationary energy storage products.

Now Hughes’ new findings raises a few questions about the actual capacity of Tesla’s battery packs.

Hughes has been running tests on cells from a “85” kWh battery pack, which had less than 1000 miles or 5 charge cycles when he started tinkering with it.

In a new post on TMC this week, Hughes claims Tesla’s advertised 85 KWh battery pack actually only has a capacity of up to 81 kWh and ~77 kWh usable range after accounting for 4 kWh of “anti-brick” buffer.

He pointed out that the battery cell counts in the now discontinued “60” kWh battery pack and the “85” kWh battery pack don’t add up.

Hughes broke down the cell counts in each pack:

  • 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.

Based on this break down, the cells in the “60” kWh packs should contain 11.161 Wh of energy, while the “85” kWh packs should contain 11.965 Wh of energy, but when tested, cells from both packs averaged 11.36 Wh.

If you extrapolate Hughes’ findings by multiplying the number of cells by the average capacity, you end up with 80.7 kWh for the “85” kWh pack and 61.1 kWh for the “60” kWh battery.

Hughes then verified these results by comparing them to the usable capacity of his Model S and Tesla’s own Battery Management System (BMS) reported 76.5 kWh of capacity after a 4 kWh buffer.

As Hughes points out, rounding down 61 to an even 60 makes sense, but how and why Tesla would have rounded up 80.7 to 85 is a mystery. We have reached out to Tesla for a comment on Hughes’ findings and we will update this post if the company decides to comment.


Update: A Tesla spokesperson sent us the following statement:

“The battery pack in Model S is designed to meet everyday driving needs as well as provide long range for road trips. The total available energy from a battery depends greatly on conditions and can vary based on factors such discharge rate and temperature. It is very difficult to replicate the exact discharge profile at home to extract the maximum available energy in a battery pack.”


Here you can watch a time-lapse of a tear down of one of Hughes’ “85” kWh battery pack:

Now it would be important to note that even if all these findings turn out to be correct, it wouldn’t change much of anything for the average Tesla owner. The company advertises both the energy capacity and the estimated range of its battery packs. Most buyers are only looking for or only care about the range, which gets tested by the EPA and is not being challenged here.

What is interesting here is that it gives us some perspective on Tesla’s battery pack ratings, which are notoriously the highest capacity battery packs of any production electric car on the market. At the moment, Tesla officially offers 70 kWh, 85 kWh and 90 kWh battery packs, though it recently started discontinuing the 85 kWh battery in certain markets.

The second best is the electric Mercedes B-Class’ battery pack, which is rated 36 kWh, but guess who supplies Daimler with this battery pack? You guessed it: Tesla.

Most electric car manufacturers advertise the full capacity of the battery pack and not the usable capacity. For example, the Nissan LEAF’s 24 kWh battery has a usable capacity of about 21.3 kWh. The difference with Tesla based on Hughes’ findings is that not only the usable range is not 85 kWh, but also the actual full capacity could be significantly less than advertised.

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  1. BEP - 7 years ago

    Class action incoming.

    • thegamingart - 7 years ago

      This really irritates me as a model s owner. Their rated mileage is over by at least 20 miles (hands down) and they clearly have false advertising on battery size. I’d definitely say a class action lawsuit is justified, especially at the price of these cars. That capacity is a 5k difference.

  2. WalksOnDirt - 7 years ago

    This makes me wonder about the 90 kWh packs. They may not be as close to ’85 kWh’ packs as it would appear.

    • Anon - 7 years ago

      According to a comment by the guy who measured the 81kWh capacity (wk057), the 90kWh packs are probably pretty close to 85kWh. For real this time. 😀

  3. Michael Myers - 7 years ago

    Class action. Sure. Make $120 for yourself, make a law firm richer, and hurt Tesla. Great plan.

    • Hellscreamgold - 7 years ago

      Why not? If Tesla is ripping people off.

      In the end, Tesla isn’t helping the auto industry much. All their stuff is overpriced…an when you take into consideration the carbon emissions from making the car and battery packs, it’s not really much better for the environment.

      • Eric Zucker - 7 years ago

        This was independently verified, a Tesla is less harmful than a comparable ICE over its lifetime, including production, usage and decommissioning, even if powered from coal generated electricity. With a renewable electricity source, the balance is obviously far more favorable towards the Tesla.

        Tesla is not there to help the auto industry, it exists to prove electric mobility can replace traditional ICE mobility for most of us. As governments see the result, they will raise the bar on emissions limits, and force auto makers to create better, cleaner cars, the compliance gimmick isn’t enough. It’s better for all of us.

  4. Holger - 7 years ago

    Not a factory fresh pack – after 5 cycles you must expect 2-4% capacity loss. Also there has be production variability taken into account… +/-3% would be pretty good. 81 kWh for a single pack falls well withing this range. Nothing wrong here.

    • R3D - 7 years ago

      2-4% loss after cycles??? Come on!!! Then the 60 kWh pack should be about 65 kWh originally. Don’t you think? Why wasn’t it advertised to 65?

      Anyway, I don’t care much about it. The only thing matters is the real world range.

      • R3D - 7 years ago

        * after 5 cycles

      • Holger - 7 years ago

        ” Come on!!! ” – that all Li-ion batteries lose 2-4% capacity in the very first cycles is really very old news.

      • Holger - 7 years ago

        But I do not disagree that TM could be more specific and state how much kWh is actually available for normal driving… like 77 kWh usable for the nominal 85 kWh battery.

      • Joachim - 7 years ago

        NO! Li-Batteries are gaining 2-4% After the First cycles! Not loosing…… And While driving several Model S’85, I always noticed a max. of 76 kWh of usesble Energy, which ofcourse Limits the range down to 422 km’s with 180 Wh/km…. The real use was 205 Wh, so we are with 90% and 10% of 76 kWh on a practical Range of 297 km’s…..

  5. Broken Portal - 7 years ago

    Lack of grasping battery capacity is not static with usage nor linear over time, makes people assume the worst.

  6. kipowsky - 7 years ago

    Isn’t this just a bit like a 16 GB smartphone, where the actual usable space is more like 12,1 GB? I know memory and power ain’t the same ballpark, but I mean that companies always have rounded up actual available space/power/capacity and we’ve all seem alright about it? It’s the game of the business, sort of?

    • Julien Gélinas - 7 years ago

      Not the same indeed. 12,1 GB for a 16 GB comes from the space the OS uses on the flash memory, plus there’s always the thing with using 1000 MB = 1 GB which isn’t true, and the file format which can make you “lose” more capacity, but at a fixed number. The present case is more related to how to discharge test was done, which doesn’t necessarily account for several physical phenomenons varying in time and space.

      But yeah, I agree with you that companies, and should I say customers, prefer to round up stuff so it can be better sold/understood.

  7. Electric - 7 years ago

    Every battery pack in electric car has 9-10% nonuseable capacity. How much is 90% from 85? In LEAF that nonuseable capacity is 88,75%.

    • Electric - 7 years ago

      In LEAF that useable capacity is 88,75%.

  8. Electric - 7 years ago

    Does this test considered the heat from discharging the battery?

    • Holger - 7 years ago

      That is a very good point… at what temperature were the tests done? Measured capacity is very temperature dependent – not that you actually lose capacity, but at not optimal temperature the ions simply do not want to move.

  9. jw - 7 years ago

    Lithium ion battery capacity actually increases during the first +/- 100 cycles, so testing a “New” battery after just 5 cycles does not mean that will be close to the full capacity. The artical also fails to mention how many cycles the 60 kWh battery had before the test.
    This image is not very clear:
    (different type of battery, but the effect is shown clearly: )

  10. Nøderak - 7 years ago

    pretty stupid to blur out the words TESLA on the side of the plywood, when you don’t carry it over through all the frames. slow it down to .25 and see it briefly flashed as he lifts off the board.
    We thought he bought it salvaged, unless this is another pack. Anyway, why hide it’s Tesla sending you batteries, was it stolen out of a warehouse?

  11. Jeffrey Hudson - 6 years ago

    Despite Hughes’ findings the only thing that matters to a Tesla driver/owner or any EV owner is how far the vehicle will travel before requiring charging and just as important the ability to do so reliably and consistently. As a Tesla owner I can attest to the battery travel distance claims of Tesla both in terms of reliability and consistency from any starting state of charge.


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