why only 85 kwhrs for the model

why only 85 kwhrs for the model

So in 2011, the 85 kw battery, and 4 years later, still 85 kw.

It is often stated that energy density increases by about 8 percent annually, so by this measure alone, that same battery pack should be punching at 32 % higher. That might be about an extra 27 kwh, or 110 kwh as opposed to an 85 kwh one.

So the question is did they just use less cells? Or does it take more than 4 years to bring the new batteries online? Or are we in a improvement rate slump?

I find it hard to believe that if it had these improved density batteries, that it wouldn't use them to improve the range of the top 2 models range.

So what are the forces at play here?

Maybe the x has them and will announce a 110 kwh battery with the enhanced range?

vandacca | July 28, 2014


I don't believe that the current Model X reservation page is up-to-date. What I mean by that is the page was created a few years ago with the expectations at that time. They have made some minor updates (e.g. making AWD standard), but I doubt they will make any significant changes until they have finished the design.

Battery improvements can come in higher densities (more power in the same footprint) and/or longer life (e.g. more recharge cycles). LiPo batteries have better life and can be molded into custom shapes, but their densities are not as high as Lithium Ion batteries.

If Tesla is able to utilize battery improvements with densities, they can do it in one of two ways:
(a) Increase the power density in the same area, thereby have a 100+ kWh using the same area. This would likely increase weight, which will reduce some of the range added by the bigger battery pack.

(b) Increase the power density, but keep the same kWh, so the number of batteries is reduced and so is the weight. This would improve range, despite having the same kWh stats.

It's unclear if Tesla can take advantage of any battery improvements at this time, but I suspect that when the site is re-designed, the final specs will be revealed and we'll understand what Tesla is able to do with the Model X.


DTsea | July 28, 2014

Ummmmm..... because they haven't redesigned it since they can sell all they build anyway?

8% is notional anyway.

Iowa92x | July 28, 2014

I bet base is 85 kWh and 100 will be optional on za X.

wangpj | July 29, 2014

I am dreaming like this:

Wish the model X 85 has same price with model S 85.... :)
model X 110 has same price wich model S P85 ^_^

[Wish they provide 110KW version]

Bubba2000 | July 29, 2014

Just looking at the Model X side by side with Model S in the front, tells me that the X is going to have a lot more drag that the S. 25-30% more in the highway? Not sure about the weight, especially of Tesla improved structural design. For such a bigger auto, I expect bigger battery. Tesla could fully populate the pack and get to 100 KW-hr to achieve the same range as the Model S?

I got a SigX reservation, but I like my P85 with its low center of gravity, acceleration, handling. May be just go for the next version of S with AWD, Autopilot and hopefully improved range? Got to test drive the X before making the decision.

Brian H | July 30, 2014

1.08^4 =~ 1.36, btw. The changes will be "lumpy", and seem to depend partly on Panasonic, which will be installing the cell mfg equipment in the GF.

carlk | August 2, 2014

85kWh may still be the sweet spot since battery supply is still the restrain. It might not make economical sense to sell less cars with larger battery capacities.

vperl | August 3, 2014

125 KW has been talked about, but fantasy is not reality

Brian H | August 4, 2014

After the GF is built, TM will have much more "optionality", which Elon says he likes. ;) | August 5, 2014

Some thoughts on batteries, battery packs, and kWh rating:

1. Here is a quote from a Wikipedia article on Tesla batteries: "Industry produced about 660 million cylindrical lithium-ion cells in 2012; the 18650[clarification needed] format is by far the most popular for cylindrical cells. If Tesla meets its goal of shipping 40,000 Model S electric cars in 2014 and if the 85-kWh battery, which uses 7,000 of these cells, proves as popular overseas as it was in the U.S., in 2014 the Model S alone would use almost 40 percent of global cylindrical battery production." If Tesla builds 50,000 cars in 2015 they will need about 355 million Li ion cells. When they ramp up to hundreds of thousands of cars a year they will need billions of cells, completely eclipsing the total production of all such cells in the world at this time. As a result, they will vertically integrate the local (US) manufacture of the cells for cost and logistical efficiency.

2. Batteries are tricky electrochemical devices with properties that are not completely understood. They have two electrodes and an electrolyte that is a chemical soup of multiple ingredients suspended in a porous inert medium that facilitates the movement of Li ions back and forth between the electrodes. The efficiency of the charge and discharge process and the energy density of the cell are controlled by the construction of the the electrodes and the ingredients in the electrolyte. It appears that Panasonic and Tesla have found a combination that promises long life with relatively slow aging subject to environmental conditions and to charge/discharge cycles and rates. It takes years to test batteries to determine the effects of changes in the electrode structures and electrolyte recipe on performance. Therefore, batteries evolve slowly compared to microelectronics for example.

3. Because of 2. above Tesla is unlikely to monkey with a good recipe in the short term. This means that the Models S and X will enjoy the current recipe in 2015 in all likelihood. Going for economies of scale would favor the same 85 kWh battery assembly for both cars or at most a very conservative variant. This would mean all the battery packs would have all the same wiring and parts. The assembly would be the same for all cars. The externals of charging circuitry, software and hardware would be the same. Assembly in the vehicles could be the same for S and X, although X will have wiring and circuitry externals to accommodate two motors. The temperature management of the pack would have the same hookups, hardware, and software. Very efficient.

4. Possible secret sauce: on the recent 2Q14 results conference call Tesla CTO J. B. Straubel slipped in a few remarks about possible changes to form factor of the individual battery cells. This could have been sly misdirection on his part but let's think about the possibilities. Panasonic/Tesla use the 18650 cell, a little bigger than AA, about 18 mm in diameter and 65 mm high. Mr Straubel mentioned possibly changing the diameter or the height of the cell. Alternatively the cell could have a square cross-section 18 mm on a side and 65 mm high. An increase in the diameter or height of a cylinder produces the same relative increase in volume. I suspect that cell energy capacity is roughly proportional to the volume of the cell. Increasing the diameter by x% doesn't seem likely because it would increase the width and length of the battery assembly both by x%. This would case a redesign of the chassis, axles, etc. that would require major retooling of the cars. Changing to a square cross section is interesting because you get about 4/Pi increase in electrolyte volume and electrode surface area in the same overall battery pack assembly, an increase in capacity of about 27% or 23 kWh in the same space, a 108 kWh capacity. Of course this would turn Panasonic's battery production tooling upside down, not likely to be a short term solution when you're trying to make half a billion batteries in 2015. That leaves battery height---hmmm.

5. Suppose you made the modest change of creating a "22650" cell, say, a cylinder that is merely 4 mm taller than the current cell, less than 1/6 of an inch. If you made that change, you would at most have to modify the vertical wall of the current Model S assembly. It is doubtful that you would have to alter anything else to cram in a box that is only 1/6 inch higher. Panasonic would have to retool but not radically since it is still a cylinder and the volume of production easily amortizes the cost of the change. This would create roughly a 22% increase from 85 kWh to about 104 kWh. Thinking ahead, this might be a good idea for the model 3. Who cares if it is 1/6 of an inch higher, if you can increase the capacity of the battery in the same horizontal footprint. Of course the battery pack just gained 22% in weight so range might only go up by 15%, I'm guessing. This would create a 300 mile plus EPA rated Model S and would help the Model X. Worth the effort, I think.

Sorry for the extraordinary length of this post but, as I said, batteries are tricky. What do you think? | August 5, 2014


Obviously if you change the diameter of the cylinder, you change the volume in proportion to the square of the diameter, a less radical change that might be tractable. This might be an easier change for Panasonic to accommodate. I still favor changing the height. Sorry about that.

Iowa92x | August 5, 2014

Does anyone know what the rough weight breakdown is per battery cell? I'd think the metal casing on each cell x 7000+ adds up to several hundred pounds. Not much can be done to reduce electrolyte weight, but one has to think reducing the casing mass could bring down the pack weight.

Larger but fewer cells means less casing metal weight.
Could a composite/plastic material be used instead (inexpensive, light and strong)?
Bundle multiple batteries into one metal casing?

I'm sure Tesla is looking at this, and there is a safety and possibly fire resistance issue with some of the above.

Solarwind | August 5, 2014

100 +KW would be a big plus for us for the X. The closest SC (at present) is 250 miles with hilly terrain, if the efficiency is less then S as expected, the 85KW would provide a huge pucker factor. | August 5, 2014

Here's an example Panasonic data sheet:
Don't know if this is the one Tesla uses but it illustrates some of the complexity of these little guys..

Weight is about 50 grams. Total Tesla weight of cells, not including packaging et al, would therefore be about 355 kg or about 770 pounds. If you add 20% to that! that's another 154 pounds, not awful but I'm sure that Tesla's engineers have worked very hard to trim out less than that.

It would probably take at least a year to get a modified form factor cell ready for production (guessing).
There would have to be a lot of testing to certify the new design.

Red Sage ca us | August 5, 2014

georgehawley: I'm pretty sure the proposed change was for a 10% increase in battery cell diameter and a 10% increase in height, not either or... The cylindrical shape is necessary to allow the flow of coolant around the batteries, carrying away heat to extend life and prevent thermal runaway.

Iowa92x: I think the cell format that Tesla uses already forgoes the metal shield. The 'metal casing' used is the battery pack itself.

Iowa92x | August 5, 2014

I think you are right Red, have you seen that RAV 4 Toyota/Tesla battery breakdown pics posted to the "other" Tesla forum?

Red Sage ca us | August 5, 2014

I remember seeing a bare cell, but I'm nit sure where... Maybe a video? | August 6, 2014

Thanks, Red.
Mea Culpa... Reminder to self: Don't post when jet-lagged

Capacity seems to be proportional more to cell diameter than volume so maybe it's electrode surface area that is the metric of importance for capacity with everything else constant.
You are right about the space around the cylinders playing a role in cooling. Li ion batteries are apparently quite sensitive to the environment and can experience thermal runaway under the wrong combination of conditions.

Another mistake I made above: 20% taller cell means adding 13 mm to height, more like half an inch than 1/6. Still, that's not huge. Maybe that's the low risk way to 100 kWh. | August 9, 2014

Listening again to the recent conference call at about the 27th minute, Mr. Musk specifically mentions three changes to the underlying cell in the battery pack in an attempt to "optimize it for automotive applications". He mentions maybe a 10% increase in both diameter and height as well tweaking of the chemistry. When the investor bores in and asks "Are you really changing the chemistry?", it sounds like Mr. Musk starts out to say yes and then he and Mr. Straubel kind of mumble simultaneously and go to the next question. Mr. Musk says that the cell changes are volumetric and in the 30% area. As I noted above, increased cell height looks to me to be easier to accommodate than increased diameter. 1.1 cubed is about 1.33. They talk about increasing energy density which may mean lowering the cell count, potentially limiting the impact on physical design and added weight. Maybe 30% increase in capacity to 110 kWh is possible within the same approximate form factor, adding maybe 150 to 200 pounds to vehicle weight. This would be enough to propel Model S well over 300 miles range and push the heavier, more air resistant Model X over 250. Maybe Model X will offer 85 and 110 kWh options.

Red Sage ca us | August 9, 2014

I'm still hopeful that a future 85 kWh battery pack would cost less and weigh less. I also look forward to a higher capacity, perhaps 135 kWh that weighs the same as today's 85 kWh, but costs about the same, perhaps marginally less. When I hear 'improved energy density', that says to me more storage in less space, at a lower weight, and reduced cost. I don't care how they manage the feat, but I believe Tesla Motors will find a way -- at least five years ahead of most predictions -- because they are progressing at twice the rate of competitors with BEV technology.

holidayday | August 13, 2014

One thought I had was:

What if they CALL it 85 KWH, but it's really higher, but hidden?

It's like the "40" being a software limited "60". What Tesla could do is make an "85" software limited version of a "90", but with a reserve for battery management that makes the battery last much longer.

In all respects, it's an "85", but inside, it's more complex.

Red Sage ca us | August 14, 2014

I'm very optimistic that most battery packs that are currently called '85 kWh' capacity are actually a wee bit higher, even today. Of course, whenever I mention something of this sort, I'm told there is 'no way' Tesla would just give away capacity 'for free'. In fact, I'm pretty sure that even from the outset the 85s were more like ~88.9 or so, and have been improving since... | August 14, 2014

I'm sure that 85 is a number somewhere on the probability distribution of all such battery assemblies. Each assembly has 7104 Panasonic 18650 cells that are all slightly different from another with capacities in aggregate that fall on a Gaussian curve due to the law of large numbers. If you multiply nominal cell voltage = 3.7 times nominal cell current capacity of 3.2 Ah times 7104 you get 84 and change kWh. Maybe they rounded up. Anyway, I doubt that they characterize the capacity of every assembly. Too much testing. Moreover, it changes every time the assembly is charged and discharged. Pick a number and you will be correct.:-))

Remnant | August 22, 2014

The game changer is likely to be the Ryden dual carbon battery.

- It offers energy density comparable to a lithium ion battery.

- It charges 20 times faster than lithium ion batteries, operating above four volts.

- It can be inserted directly into existing manufacturing processes without retooling. Thus, Power Japan Plus will begin benchmark production of 18650 Ryden cells later this year at the company’s production facility in Okinawa, Japan.

- Because it does not contain rare metals, [the] manufacturing of the Ryden battery is under no threat of supply disruption or price spikes.

- It has been rated for more than 3,000 charge/discharge cycles.

- By eliminating the unstable Lithium oxide used in the Li-ion batteries, it greatly reduces fire and explosion hazard.

- Due to minimal thermal change during operation, it eliminates the threat of a thermal runaway and the need for complex, heavy, and power hungry cooling systems.

- Finally, the Ryden battery can be 100 percent charged and discharged with no damage to the battery.

Gen3Joe | August 23, 2014


I'm looking forward to seeing the team Taisan demonstration car in action. Until then I remain skeptical.

If real and cost competitive this will be huge. The company is claiming an above 4 volt operating voltage and 100 ah/kg which would mean at least 400 Wh/kg an impressive ED to say the least.

Iowa92x | August 23, 2014

Good stuff Remnant, hopefully it comes true soon.

Brian H | August 23, 2014

Tesla requires only 1 working prototype to investigate. No takers from the various miracle battery boosters to date. None expected.

jjs | August 23, 2014

+1 Brian H. | August 23, 2014

Once proven to be viable in lab tests, new battery designs and compositions have to go through lengthy environmental and charge/discharge life tests. Even if the Ryden battery is for real, we're not likely to see it in EVs for a few years. I hope it is real.
Still, today's Superchargers operate at 120 kW, providing 300 Amps of current at 400 volts DC. Charging 20 times as fast would require the same battery configuration to tolerate something like 6 kiloamps! That's a lot of current.

DTsea | September 2, 2014

+1 Brian h. The ryden 'battery' is still in the popular science magazine article phase.