Increasing pack by increasing cell storage

Increasing pack by increasing cell storage

Hmmm, I'm wondering, if the width and length of the battery pack is fixed, and the energy density per gram is fixed, the battery pack could theoretically be increased by making the individual cells 1/8 inch or 1/4 Inch longer (higher). It would make very little change in the design of the car and could go a long way to getting more bang from the same horizontal plane.

Hell even a 1/16 inch may make enough difference when talking so many cells.

JPPTM | 18. august 2014

This has been discussed elsewhere (use to search and also go to TMC and look through the forums there). The 18650 size is a product of a preexisting form factor. The size could be tweaked, even the shape (hexagonal vs. round). I would assume that there are lots of smart battery engineers at TM looking at all angles.

Grinnin'.VA | 18. august 2014

@vgarbutt | AUGUST 18, 2014

"Hmmm, I'm wondering, if the width and length of the battery pack is fixed, and the energy density per gram is fixed, the battery pack could theoretically be increased ..."

The smart-ass answer to your question is: If everything about the battery packs remain unchanged, new battery packs will be identical to the current ones. Since I don't think you deserve a smart-as response, here's what I think:

JBS has discussed this publicly this year. As I understand his statements, the key points are:

1. The MX will use battery packs that could fit on the MS. The dimensions of the packs are fixed.

2. Tesla's research has concluded that the ideal dimensions of a Li-ion battery cell for BEVs are about 10% bigger than the dimensions of the cells in the current MS battery packs. I interpret this to mean that Tesla will not use such an 'best-size' cell for the MX. I presume that they will use such a cell for Gen3. But that's me speculating, not based on any direct statement by JBS.

3. Tesla has an ongoing battery research/development effort. They have found improvements in the content of the cells (cathode, anode, 'soup', etc.) that enable them to increase the battery energy density by roughly 7%-8% per year. JBS sees no reason for this 'battery chemistry' improvement to slow down in the next 10-20 years. I interpret this to mean that Panasonic could make newly designed battery cells with their latest proven 'battery chemisty' for Tesla whenever they choose, subject to possibly a year's delay from decision to availability of the first new batteries.

Most likely, in 2017 they could use newly designed battery cells with about 40% higher energy density than the ones for MS packs. I presume that such battery packs could be designed to work with both the MS and the MX. If this is true, Tesla could deliver a 119 kWh MS/MX pack then. Such packs would use the current cell dimensions and fit in the current MS85 battery pack containers, presumable arranged and cooled/heated just like the current MS85 pack. Of course, they would almost certainly generate more heat. So they might need to 'beef up' the battery cooling pumps.

Another important thing about such improved battery cells is their costs. AFIK, Tesla hasn't said anything directly about whether changing the 'battery chemistry' would increase or decrease its costs. I'm inclined to assume that it would not significantly increase the cost of a battery cell. Why do I think that? Because Elon is on record saying that he would be surprised if it takes Tesla 10 years to reduce the battery cost per kWh to $100. To me that means that Elon expects $100/kWh Tesla batteries to be available no later than 2022, 10 years after the first variant of the current battery cells. The estimates I've seen for the cost per kWh for the current MS battery packs range from $230 to $400. Together JBS's and Elon's statements make sense if the battery cell costs remain stable except for the projected 30% manufacturing efficiency improvement for the GF and Tesla's battery packs use improved battery cells with higher energy density.

The question of when Tesla will introduce higher energy-density battery cells is a bit hazy. AFAIK, they aren't promising to do so at any specified time. I believe they will do so at some convenient time when they have tested improved batteries enough to be confident that they will work well. Why? Range anxiety. Many people (including me) would dearly love to have battery packs that would have a range of about 300 miles in an MS is driven at typical freeway speeds under typical conditions. I hope to get my MS85 battery pack replaced by such a battery pack soon after Tesla offers them to existing MS owners. I'm willing to pay $$$ for that upgrade. They could repurpose my old MS85 pack, recondition it and sell it with the same warrantee as the new MS85 packs, or whatever. I just want to cruise down the freeway without needing to slow down to avoid unwanted delays for charging. Also, consider the MX. It will be taller; it will have a higher drag than the MS. So with the same battery pack as an MS, the MX will have a shorter range. I don't think most prospective MX buyers or Elon will be satisfied with that for very long. When they can offer a higher capacity battery with at least the range of the current MS, I expect them to do so.

This interpretation/projection calls for progress at a healthy clip on battery capacity and range. I believe I have included only modest, responsible projections. But I'm sure that some people do not expect such progress in the next few years. I invite any/all who may think I've been overly optimistic, or that I've left out any important information: Please tell us what you think isn't realistic; please share with us your insight of the subject.

Go Tesla!
Ron :)

vgarbutt | 18. august 2014

Thanks, question answered.

You all rock.

JeffreyR | 03. september 2014

Ron @Grinnin':

I think you and @Red Sage have understood and communicated EM/JBS's comments on battery improvements very well. I've watched JBS's video on the subject and agree w/ you both. There is @RS's theory that they are already testing new batteries in the different versions of the battery pack. They could limit exposure of this in software or depopulate cells to save cost and weight.

What I would add to the mix is the transitition period around the release of the MX and M≡. Tesla is already production constrained. They sell every car they make. So I do not think they will change battery pack options w/ the MX (though it is possible). I think they will/are reducing the number of cells in the pack. But I think w/ the M≡ and the Gigafactory they will release a new set of options. The M≡ will get the old 60/85 kWh rated packs (w/ an increased range due to lighter weight) and to differentiate the high-end models they will get your boost in capacity. I think they will keep the rounded 5/10 capacity so your 119 kWh will be 120 kWh. Other than that I agree w/ your estimate (while holding out hope RS's pipe dream of 135 kWh comes true).

Grinnin'.VA | 04. september 2014

@JeffreyR | SEPTEMBER 3, 2014

"I think they will/are reducing the number of cells in the pack."

Sure, when they have higher density cells, the obvious way to stretch the limited supply of cells is to use fewer cells per battery pack. But IMO they will have good reason to increase the capacity of the optional high-end battery packs also. That's because we have plenty of MS owners who like to drive 80 mph or faster on the freeways. The current MS85 limits the range of such free-spirited rides, forcing them to stop for charging more often than most of them would prefer.

Elon is emphatically committed to provide cars that are 'fun' to drive. Before the end of this decade I expect Tesla offer higher capacity batteries, not just higher density battery packs with fewer cells and no improvement in the range.

Ron :)

P.S. I hope to buy a higher capacity battery for my MS85 when the battery nears the end of its useful life. I'm one of those guys who wants to charge down the freeway, going with the flow, without requiring multiple charges on the road the same day. Do you know any other Tesla buyers who share that desire?

vgarbutt | 04. september 2014

If the model S manages to last more than 10 years gracefully, ill bet ALL owners that can, will get a new battery, and use the old battery as a trade in.

Guy2095 | 04. september 2014

I still think that when feasible the Model S and X will get a refresh bump from 60/85 to 75/100 with a follow-on, premium priced, grand touring option of 120 or maybe 125. This makes the 60 25% better but still not as good as the prior 85 and boosts the 85 to that longed-for 300 real-mile range. The GT of course then goes twice as far as the original 60. This all certainly seems worth shooting for if it can been done Tesla soon.

Remnant | 04. september 2014

Coolant circulation takes up space. Only a battery improvement that makes it more stable thermally could allow a change to a hexagonal or even square section, in which case the coolant volume could be reduced as well, resulting in less weight.

The battery itself could become lighter also, such as in case of a lower metallic content, even without changes in the form factor. Elon has mentioned a likely improvement in the electrode materials.

The obvious candidate for these changes is the Ryden, or dual carbon, battery, as soon as it becomes production ready.

The Ryden battery has recently been tested by Team TAISAN in its vehicles.


Red Sage ca us | 04. september 2014

JeffreyR: In my dreams, pipes only blow rainbow soap bubbles. ;-)

Grinnin' Ron: Opponents of the Battery Swap concept insist that Tesla Motors will not allow even those who want to upgrade from a 60 kWh battery pack to an 85 kWh version to do so, even with cash in hand. They say that the idea of either upgrading on the road temporarily or at the 'end of life' will never be possible or allowed. I disagree with them, of course.

I think that Tesla Motors simply wants to make sure that everything works, and that there is a reasonable opportunity for Customers to upgrade at an affordable rate.

JeffreyR | 04. september 2014


I do think all drivers would like more range. I was merely commenting on my guess for the timing. An increased range option could happen w/ the MX, but I think they'll wait for the M≡ and the Gigafactory before they do. There may be enough of a demand that you could "trade in" your 85 kWh pack to subsidize your 120/135 kWh pack before it's kaput.

Larry@SoCal | 04. september 2014

Few need more range / bigger battery for daily use. Even the 80 mph ones of us do not need more battery for local use. We need more SuperChargers.
Wasn't that the original intent?

Red Sage ca us | 04. september 2014

larryrhoades: The need/want profile changes as people realizes how much they prefer using electric cars. The main thing that is solved by having more range is that since it is gained by having more capacity, using the Superchargers becomes faster at the same time. That is to say, the 50% recharge in 20-30 minutes will be true even at higher capacities.

At ~250 miles of total range, you gain ~125 miles in that time frame. At 400, you get back 200. At 500, you achieve 250, and so on.

If for instance, you had a battery pack that gave you a range of 1200 miles, that means that for the vast majority of road trips you would not be stopping to charge. You would stop to eat, use the bathroom, do some shopping, watch the sunset, take a nap... and charge while you were doing that, to 'top off', rather than 'fill the tank'.

Thus, the final barrier to adoption of electric cars would be removed forever. That is why more range is needed more than anything else. To shut up Naysayers. | 05. september 2014

Hmmm. Let's see now. If the Supercharger is limited to 120 kW, and the car uses 300 watt-hours/mile regardless of battery capacity, I'm having trouble seeing how battery capacity affects miles per unit charging time, unless you are suggesting amping up the Superchargers that are already delivering up to 300 amps to the cars... Help me out.
On the other hand a 1200 mile range with a full charge means virtually all recharging would be done while the driver is asleep and Superchargers would move to hotels and motels. Not a bad idea.

Grinnin'.VA | 05. september 2014

@Red Sage | SEPTEMBER 4, 2014

"That is why more range is needed more than anything else. To shut up Naysayers."

Red, I think I agree with the gist of your post.
However, I think Tesla needs more range to satisfy its customers.
I know that I'm disappointed by the practical range of the MS85. But that didn't stop me from buying an MS85 and investing in TSLA stock. I'm thrilled by all of the marvelous good things that Tesla is doing. So I don't think I fit in the 'naysayer' category.

Go Tesla!
Ron :)

killbeas | 05. september 2014


I don't think its quite linear. I haven't validated this but I don't think that the supercharger delivers the same current over the entire charging period to fully recharge a battery. As the battery becomes closer to capacity, I would think that the current starts to taper which is why it takes longer to get the higher percentages of charge.

If that is the case, you would benefit some from the longer range batteries, as the battery would normally be able to accept the limit current (of the SC) longer which translates into more energy storage per unit time during some of the charge cycle. Or in other words, the flat portion of the current curve would normally last longer into the charge cycle. This is consistent with all battery charging that I'm aware of.

So as you state, you would be limited by SC current capacity but the larger battery could accept that capacity longer into the cycle. Others may know more than me on this so take this with a grain of salt.

Brian H | 05. september 2014


As he said, "peak" delivery is ~300 mph. Prolonging the peak is key. But 120 kW won't suffice for a 10X larger battery.

Brian H | 05. september 2014

Edit: 5X larger battery.

Red Sage ca us | 05. september 2014

Grinnin' Ron: Yes, Tesla drivers will be satisfied long before Naysayers are... We can hope to quiet them to a low grumbling in the background, heard only amongst themselves.

jbob | 07. september 2014

Oak Ridge National Laboratory is working on two projects funded by the DOE to improve battery costs and capacity.

- Manufacturability Study and Scale- Up for Large Format Lithium Ion Batteries
- Overcoming Processing Cost Barriers of High- Performance Lithium-Ion Battery Electrodes

Not sure if Tesla is eyeing these projects, but if they are racing to increase capacity and reduce costs, i am sure they are aware of everything currently being researched.

Advancements and findings from these studies will have an impact to Tesla, or it's competitors.

Hopefully, natural graphite is found to be a key driver for the lower costs and improvement in capacity, as that will have a profound impact in reducing the environmental impact of synthetic graphite and make the Tesla vehicle even greener.

Note: Zenyatta Ventures' Albany Deposit (not yet a producer) is a raw material supplier of graphite being used in these studies. Probably chosen because of the very rare and unique formation of this hydrothermal deposit. See more at...

bonaire | 07. september 2014

It would be foolish to deliver a battery sized > 100 kWh and not try to get to smaller, lighter and fewer cells so that the car can lose 400 pounds at 85 kWh with the M3 being about 50 kWh for most people's needs. Many of us need far less than 85 kWh daily. Many want it for the occasional trip or peace of mind. Others want it so batteries go through fewer cycles and have longer life. If battery recharge count can go up three times, full battery pack sizes could drop to 50 or 60 kWh and you can cycle them more with less input cost to the car. The idea is to get more people in EVs, right? then the cost has to come down. 85 is a "cadillac feature" and not needed. What do most people drive on a daily basis? Triple that and it gets real comfortable to decide to buy an EV. If someone does 40 miles a day, 120 mile range is not scary. But the consumer thinks with outliers in mind and then "need" to have the 85 kWh "just in case". And then they say "if I cannot buy an EV with 300 mile range and 5 minute recharge for $30,000 then I am sticking with my ICE". Bigger batteries are not the problem - price and charging convenience is the problem.

Red Sage ca us | 07. september 2014

bonaire: I believe that 60 kWh should be the baseline minimum for all Tesla Motors products going forward. That way, someone who starts out on a Monday, with a full charge, and a 250 mile range, can do their 40 mile round-trip commute & daily driving for the whole week and still have ~50 miles of range left. They can top off at a Supercharger on the weekend, once every week, if they don't have charging at home or at work.

I believe that as battery packs get denser energy battery cells within them, the weight will come down. But at the same time, there is a certain maximum weight that will not cause issues given a certain amount of stored energy. I believe that Tesla will find the proper balance and make it work.

Over time, the cars will weigh less, have battery packs with higher capacities, and have much longer ranges. There is no reason to set an artificial 'upper limit' on maximum range. The better that technology allows the cars to be, the better they will become.

Grinnin'.VA | 07. september 2014

@bonaire | SEPTEMBER 7, 2014

"It would be foolish to deliver a battery sized > 100 kWh and not try to get to smaller, lighter and fewer cells so that the car can lose 400 pounds at 85 kWh with the M3 being about 50 kWh for most people's needs."

I can't speak for 'most people'. I ordered an MS85. I don't have multiple cars. I want to take road trips from time to time without needing to plan the details of my trips around when and where I can charge my battery. Unfortunately, for now the availability of convenient recharging sites restricts my road trip flexibility. I consider the MS85 range the only significant negative thing about the MS. For me range is a substantial concern.

Ron :)

negarholger | 07. september 2014

One shoe doesn't fit everybody... range options are critical for EVs

In the Bay Area for me 70 kWh (80% charge) can do all my daily trips... but leaving the Bay Area even 85 kWh is not enough. If you live in a more remote area then even 85 kWh doesn't do your daily trips.

Range vs acceptance is a S curve
100 miles = 4%
150 miles = 40%
200 miles = 70%
300 miles = 96% | 07. september 2014

@killbeas: you are of course correct that charging is not linear, especially when you get closer to full capacity. But, if, 120 kW gives about 40 kWh in about 20 minutes, that must still be on the linear part of the curve. Therefore, in 20 minutes you get 40 kWh no matter what the capacity of the pack is but in 40 minutes or so you would be able gain energy with a >85 kWh pack, assuming that the departure from linearity of the 85 kWh pack occurs between 40 and 80 kWh.

vgarbutt | 08. september 2014

My original idea was to simply add a quarter inch to the length of the individual cells to get more out of a fixed battery box footprint. Perhaps making the diameter a bit bigger will mean less cells and cheaper price per cell as well.

bonaire | 09. september 2014

Slightly bigger cell means fewer cell walls and more battery. And add slightly denser battery material. No need to make them longer.

Timo | 09. september 2014

Smaller diameter allows less empty space between cells. In order to make battery pack more energy dense you would need to do more than just change the size of the battery larger, you would need to change the shape of the battery.

That said, round short peg -shape isn't the best shape, it is just dirt cheap. With gigafactory Tesla can re-invent the whole battery pack. Make the batteries whatever shape they want.

Grinnin'.VA | 09. september 2014

@vgarbutt | SEPTEMBER 8, 2014

"... simply add a quarter inch to the length of the individual cells to get more out of a fixed battery box footprint. Perhaps making the diameter a bit bigger will mean less cells and cheaper price per cell as well."

bonaire | SEPTEMBER 9, 2014

"Slightly bigger cell means fewer cell walls and more battery. And add slightly denser battery material. No need to make them longer."

JBS has already said that the ideal size for a Li-ion auto battery is about 10% larger in each dimension than the batteries uses in the MS. He and his team are experts at this. I accept their conclusion.

Timo | SEPTEMBER 9, 2014

"In order to make battery pack more energy dense you would need to do more than just change the size of the battery larger, you would need to change the shape of the battery."

Based on JBS's statements, I expect Tesla to continue using cylindrical batteries for the foreseeable future. They have considered cells with square corners and hexagonal cells and decided that such changes would create more problems than they would fix.

The primary way to increase battery energy density is to tinker with the contents of the battery: anode, cathode, 'soup' and separator. The good news is that JBS and Elon have reported ongoing success in Tesla's battery research.

Go Tesla!
Ron :)

vgarbutt | 09. september 2014

Thanks grinnin,
Great news.

Brian H | 09. september 2014

Tighter spacing with square or hex cells makes cooling more difficult, a very serious consideration with TM's superb battery management system.

Grinnin'.VA | 10. september 2014

Brian H | September 9, 2014

"Tighter spacing with square or hex cells makes cooling more difficult, a very serious consideration with TM's superb battery management system."

Right on. There is no hint in Tesla's puplic statements that they might want to use a battery that's not cylindrical in shape.

Ron :)

Timo | 11. september 2014

At least now. I wouldn't say that they are not investigating different shapes and whole new structure of the pack for future.

Bubba2000 | 11. september 2014

Tesla must have done all kinds of studies on battery geometry. On height, diameter, internal impedance, charging+discharging performance, heat generation, heat dissipation, life of battery, etc. All this can lead to weight reduction, increase in cell storage. They are not afraid to think out of the box.

In addition,it is likely that Tesla will work to optimize to reduce the weight, size of the battery pack, heat transfer, coolant. I also expect to see decreased electrical resistance of the battery pack. Outside the pack, efforts will be made to improve the electrical efficiency in the power cabling, inverters, motor, etc.

If Tesla could reduce the weight of the autos, lees batteries would be needed.

JeffreyR | 11. september 2014
Red Sage ca us | 11. september 2014

Higher energy density leads to lower cost
Amazing how many people claim to have watched that video, but never seem to catch that point.

Thanks for reminding us to beat them over the head with it, JeffreyR!

JeffreyR | 11. september 2014

Thanks for posting the link in such a way that I can volkerize it @Red Sage!

vgarbutt | 11. september 2014

There is 2 sides to that coin. Higher energy density lowers costs, but it also allows longer range for the same weight. I don't imagine that I would start reducing mass until the range got to where range anxiety was a non- factor in the adoption equasion. THEN i would start reducing the cell count. And then the cost would start dropping.

So the question is, will lower cost, or longer range be the attribute that gives the bigger bang-for-your buck when it comes to the tipping point for mass adoption?

Red Sage ca us | 11. september 2014

Well... When a 60 kWh battery pack is so dense that it weighs 300 lbs or less, and is so inexpensive that it costs under $5,000 as a retail replacement component, mass adoption will be absolutely no problem whatsoever.

Think about it. You could have a car about the same size and shape as a Mazda RX-7. It would weigh perhaps 2,800 lbs. It would have a 300 hp/317 lb-ft torque motor. That would probably work out to an EPA rated range of 350 miles.

So yes, higher energy density gives lower cost, and greater range with the same storage capacity. I think that Tesla Motors will work toward increasing capacity first, knowing that they will get better range that way, and even more later, as density improved.

Brian H | 11. september 2014

It also increases C, power output and charging rate.

Timo | 12. september 2014

Higher energy density and higher C do not depend of each other. You might have lower C just as well as higher C with higher energy density.

You definitely want to increase both if possible. That way you just have lighter pack with everything else staying same.

Brian H | 12. september 2014

Yes, I was thinking more of capacity in total and charge rate (in kWh/h). Given the same chemistry, 50% of a 20kWh battery takes as long as 50% of a 120kWh one.

Bubba2000 | 16. september 2014

It seems to me it would cheaper to engineer the car design, use lighter but stronger materials to reduce overall weight of Model 3. Compared to battery chemistry advances it is much easier to optimize design using complex hollow shapes, combination of alloyed steel, Al alloys, Carbon Fiber, and even Titanium alloys for critical parts. Tesla already uses Ti alloys.