Could This Patent Be What Tesla Will Use for the Model E?


The E stands for economical. The Tesla Model E (like the Model T Ford) is supposed to be an EV paving the way for mass adoption. The Model E will be an EV priced in the $30,000’s with a 200 mile range.

In order to make this happen, Tesla needs a battery that is even lower cost than the one they have now. How can they do this?

Thinking in Terms of Battery Cycles

Tesla uses a high energy density battery. This high energy density battery has one HUGE disadvantage: Low Cycle Life (on the order of 500 cycles).

To get a feeling for how battery cycles work please refer to figure 2.

Tesla Patent

Figure 2

One cycle is defined as one FULL discharge cycle of the battery’s fully rated kwhs. The Volt uses 65% of its rated capacity. Each time it is fully discharged it uses .65 cycles of life. In Tesla’s case, it uses closer to 90% of the battery’s full rated capacity. For the 85-kwh version of Model S it can go 300 miles on one charge. Each time it is fully discharged it uses .9 cycles. The arithmetic is very simple and shown in figure 2.

Is Tesla Considering This Patent for the Model E?

Is Tesla Considering This Patent for the Model E?

In 100,000 miles, at 300 miles per charge, the battery would be discharged 333 times. Since the DOD is 90% this is equivalent to 300 cycles easily beating the 500 cycles of life. Just for reference, the same numbers are shown for the Volts battery. Since the Volt only gets 38 miles per charge, in order to go 100,000 miles the battery must have a cycle life of 1710 cycles…..considerably more cycles than the Tesla.

In order to get around the problem of low cycle life, Tesla increased the size of the battery until they got the desired cycle life.

There is a trade off between energy density and cycle life. Higher energy density batteries have lower life….there’s no free lunch. Also due to poor cycle life the batteries are relatively inexpensive on a per kwh basis. So we have a Tesla battery that is high energy density, low cycle life and low cost per kwh. Tesla gets around the problem of low cycle life by just making the battery very large.

What if we take this theory one step further?

Tesla Patent

Figure 3

Tesla’s patent is nothing more than a hybrid battery (why didn’t Toyota think of that). A battery chemistry similar to our Volt could be used for everyday driving (usually less than 40 miles) and would be charged on a daily basis. Due to the statistical nature of peoples driving habits, the range extender battery is seldom used and therefore can be a chemistry with very low cycle life. The range extender battery doesn’t necessarily have to be metal air. It could be any chemistry with high energy density, low cycle life and low cost.

You can see that Tesla’s patent is just an extension of the philosophy they are using now.

I will leave it up to the readers here:

Does this concept have merit? Could this patent be what Tesla has up their sleeve for the much ballyhooed 200 mile range $35,000 Tesla EV?

Categories: Battery Tech, Tesla


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32 Comments on "Could This Patent Be What Tesla Will Use for the Model E?"

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Yes, it has merit.. But I think they need to have the main battery pack have at least 60 miles of range, if not more. Because you know all of these people with long commutes that have been sitting on the fence are going to jump on this vehicle and be putting far more miles on it per day than a Leaf or a Volt get.

The cycle life description is really oversimplistic.

Yes, Tesla uses a chemistry with lower cycles (although the Model S chemistry has greater cycle life than a typical laptop battery).
Although cells have cycle ratings it’s based on a test with full cycling at a specified C-rate. But there is not a simple linear relationship between charging/discharging and cycle life. Degradation depends on multiple factors with the basics being:
– Middle of the pack is good
– Lower charge/discharge rates are better
– Temperature-controlled charge/discharge is better.
Tesla’s approach:
– Has a large pack which lowers the normal discharge rate
– Uses battery pack design and active management to optimize pack condition while in use. (Active management is the “American” approach, while the Japanese have gone for more stable chemistries with air cooling, and so far the Americans are winning).
With active management Tesla’s “300 cycles” end up being much more.

I’d suggest that the different durability requirements of the cells for long-range BEV, mid-range BEV and limited-PHEV really come more from the average cell discharge rates, rather than the usable capacity.

The hybrid battery concept is an obvious one, but the implementation is a challenge.


The REX battery would spend a lot of time unused, and should be kept well below full charge to help extend its life. One would want to charge the two batteries to full only just before a long trip (this should be selectable, as with the Leaf, but unlike the Volt). Optimally the car would bring both batteries down from ~100% to ~70-80% first before then draining the two batteries further (main, then REX). @ David: While Tesla may indeed make the range more than 40 miles on the main (if this is their approach to the Model E), I think you’re confusing the markets here: I see no reason to doubt the researched conclusion that most drive under 40 miles per day and occasionally exceed that (which the REX covers); and for those that exceed 40 daily, they’ll need something different (and have to pay more for it, i.e. a Model S). Also, I’m not sure why you think a Leaf doesn’t handle 60 daily just fine (unless you’re in Arizona) (people seem to have a way of continually shrinking the Leaf’s range past reality, which is ~75-80 for most people, and over 100 for some who drive only… Read more »

I have a Leaf and there is NO WAY I would suggest anyone drive it 60 miles per day. While yes, it can technically do it, if you factor in bad weather or detours you are screwed. This is especially true for drivers who drive at highway speeds.

I concede that 60 miles of mostly highway driving mid-winter in colder regions or mid-summer in warmer regions would likely force one outside the comfortable 18-80% charge window regularly with a Leaf. You need 4 mi/kWh to stay in that range, and while the two Leaf owners I know personally do much better than this (admittedly with only modest highway driving, in North Carolina and New York), you’re probably right that a large fraction of drivers will do worse than 4.

FWIW, I cannot get 3 mi/kWh during the winter on the highway in upstate NY. For the months of Dec-Feb, I average about 2.5 mi/kWh.

*This is with the 2012 Leaf, without a heat pump. I cannot use the heated seats either, because I have two small children in car seats. I cannot speak for the 2013 Leaf with heat pump.

Last fall when i had my ’12 LEAF SL my commute was 72miles RT, I did it every day with no issue, backroads at 45mph with one 3mile stretch of Hwy…again zero issues. winter got rough, wife decided to keep the car for city driving and I took the gas guzzler. Tottally defeated the purpose on using the EV as a commuter but a slightly larger battery would of allowed some heat to be used and a perfectly dooable commute.

Most people would be uncomfortable with that commute, a 88mile trip to baltimore on weekends and public L2 Charging at Walgreens allowed for free trips home…again simple with planning. But yes majority of people will stay under 60miles for comfort and their own sanity. 🙂

Assuming the REX battery is rated for 160 miles (200 total – 40 main), would the solution to extended REX life be to have a 230 mile battery, but only charge it to 70%?

If 200 miles of AER is the starting recipe, swapping in 40 miles of higher-life battery will only make the model E more expensive.

.. and you’ve basically lost Supercharging and performance.

Metal-air has low power-density and low efficiency, which means you really don’t want to use it much. And they gain weight when you use the battery, so you’d have to balance that.

It also tends to generate heat when you use it. If only the need for extra range was greatest when you also needed warmth…

I don’t see this as Gen 3. I see this as a Gen 4+, when Tesla goes for world domination and wants to expand into a low-cost mid-range BEV market.

I am thinking the same, as in my post here this Metal-air is not for Gen III but for future Gen IV, very low cost entry level electric cars that will push ICE cars into the classic cars sector.

I think what they are saying is that the small battery will cost more, but they’ll be able to make the much larger battery cheaper (by having less cycles than the “starting recipe”), which should result in a net savings.

If less cycles for the standard Tesla battery means even greater energy density (consistent with the article), than performance wouldn’t necessarily be given up. But how accessable is the downward cost curve on such a battery, or 18650 cells which are more dense, and cheaper?


The possible business model I see is that the extendend range battery would be a fast swap pack. A completely automated swap station would install a fully charged ER battery pack for the temporary, rental use of the car owner. With that pack rental, car owners would be granted access to the supercharger network to charge the packs. Consumer makes long trip, then returns the pack to another automated swap station.

There you go Tesla. Do you have the moxie to pull this off?

I personally hope they do not follow this approach. For me, the Tesla GenIII will be replacing a long-distance travel car. I cover about 8000 miles / year in that car, but they all come as long trips (200-250 miles). The shorter trips are already covered by the Leaf. I hope they can pull off the GenIII without this battery. I’m willing to pay more for it, but I simply cannot afford the Model S.

If you make 25 long trips per year, Teslas REX battery would still last 10 years for you, assuming 500 cycles of battery life.

I don’t think this is going to be 2 different rechargeable batteries. I think the 2nd battery will be a consumable metal air range pack, use one time and throw away (recycle), to be purchased for long road trips.

I kind of join you on this. I think 200 miles will be from the main battery and indeed the extra will be the possibility to use single use additional metal air batteries coca cola bottles sized. Once empty you return them for a caution refund.

Appart from this it should be noted the the MIT likid battery could give a complete new game since it has high energy and infinite cycle life.

Thanks for the post George. The best thing that you have done is force us in the EV community to imagine other possibilities. Good on ya!

Or, they could use a extended range system with a high density fuel that doesn’t consume the fuel storage tank, like, say, … (revelation music) … an internal combustion engine! No, wait … GM is already doing that, so it can’t be a good thing.

I don’t think ICEs are totally out for REX. 50,000 happy Volt owners and BMW i3 on the way. As I have said before, it is way too early in the game to rule anything out. With over 200 ICE options available, it is clear that one size does not fit all in the automotive arena. Why should EVs be any different?

Hi, Good thinking and good questions. (I like that you used my name for the Model E from my previous post. I will like it to be called Model E in real life too). I do not think that the next Tesla, the Model E, will have the same specs (as range) like the Volt (40 miles electric + some gas miles), I think 40 miles (15kWh battery) is way to low for Tesla for a high cycle battery. Instead I think that the Model E will look mode like this: A 40kWh battery (low cycle) with swap & fast charge capabilities, at a price of 15k will give a light aluminum car a range of around 125 mile (200 km), combined with a 25kWh battery (high cycle) with a price of another 10k that will give the car an additional 85 mile (135 km). And VOILA a 200+ mile (125+85=210) car with a combined battery price around 25k, that will let some room for the rest of the car (basic version). This Model E will have the next optional pack available, instead of the 40kWh battery a 60kWh battery for an additional 10k. This will make the Model E… Read more »

Once again, I am going to hope that you are wrong. This would be horribly disappointing. I’m going to hinge my hopes on previously estimated prices of ~$200/kWh. With that, a 65kWh battery only costs $13,000 – much less than your calculated hybrid battery.

If the cost will be lower then this then will be even better because Tesla will be able to put a bigger battery (=more range) in their Model E, and I think we all want the biggest battery that they will be able to put in their 35k car.

One of the benefits of EVs is that they are simpler than the ICE motivated vehicles.

Let’s keep it that way.


I wouldn’t want a low cycle battery in my car, as I wouldn’t want to use it. And if I’m not using it, why would I want to carry it around all the time, let alone pay for it?
No, I would want my whole battery to be useable when I need it, without having to consider that now I only have x-1 times to use it before it becomes useless.

Too bad this blog couldn’t be titled: “Could this Operating Prototype be what Tesla will Use for the Model E?” As it is, it’s all just a fantasy until it becomes something real.

Two vehicles that run on one chemistry, and the third that runs on a different chemistry?

No, I don’t think so, economies of scale would dictate that to maintain or lower costs, all three should be the same. As I understand it, the batteries in the S are arranged in modules. it makes sense to me that these modules be sufficiently universal so that they can be integrated into each platform.

This new idea, I could see only as a range extension module that could be available in a lease per use basis.