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Anyone else surprised that new battery pack is only 90kwh?

First of all, I'm not complaining. Just mostly curious about the rate at which Lithium Ion density improvements are being made over time...

I also get that having something in the lab and mass producing it are completely different things. However, Tesla was essentially mass producing 85kwh packs in mid-2012. Now we are in mid-2015, three years later.

After reading various articles and threads like this one (How fast is lithium-ion energy density improving | Forums | Tesla Motors) stating that JB has claimed 8% year over year improvements, I was under the impression that if a new pack were to come along this year, we'd see something more along the lines of a 105kwh pack by now (3 years after 85kwh delivery @ 8% improvement per year = 107kwh). Even going by Elon's recent comments of 5% improvement year over year going forward, it seems we should still have seen a 95kwh pack (85kwh with 3 years @ 5% growth = 98kwh).

Was anyone else a bit surprised that the pack was not denser, given the previous and currently stated trajectories?
Seems to me Tesla wanted to be cautious with the application of new technology in the 90 kWh pack. Namely, not completely replacing the graphite anode with a silicon anode, but creating a hybrid of the two materials. IIRC silicon doesn't hold up as well as graphite, so using an entirely silicon anode would be bad for pack longevity.
Batteries do not necessarily follow their own equivalent of Moore's Law, as there's no one design parameter (like feature size in integrated circuits) for engineers to attack in batteries.

Rather, specific and distinct improvements can be persued in batteries. What we have here is a generalisation about how quickly they expect to validate and mass produce plausible improvements in the near future (hence the fuzziness in the numbers - 5-10%, 1-2 years.) Don't expect this to be highly predictable for decades like the I.C. fabrication business was. We might see periods of stagnation, huge jumps and everything in-between.

The Gigafactory - combined with Elon's engineering/production staff mingling policy - might make unanticipated breakthroughs more likely to happen. Unfortunately, you can't predict inspiration or know in advance what nature will permit.
I know, that in theory, more range is better, however I see little complaining from people that own 85s that they need more range than they have. Believe Tesla has hit the sweet spot here on a Range vs Cost vs weight.

Not sure an 95 pack would have much more value to actual owners than the released 90.

Believe forum people might just want bigger numbers to feel like winning something, however in the real world, the range of current Tesla cars is pretty acceptable.

I even hear from many owners of 60s that say for their needs, that is sufficient.

Kinda same with better 0-60 times. Everybody wants it, but few need it.
Yes, Only 90kWh is a bit of a set back. Explanation can be something along the lines of:

1. We ar not told the exact battery capacity. 85kwh is a marketing term and does not mean 85.000wh. It may be that when tesla specced the original battery they speeced the capacity too high and had to reserve much more than they enticipaded beforehand to meet longetivity. 85kWh may very well be along the lines of 82.000 Wh and those 90kWh may be 89.000 or 92.000 wh. We just do not know this exact numbers. But even if orignal battery is only realy 82kWh and a new one is 92Kwh, that still falls short of 8% annual growth.

2. Exact battery capacity is a bit of oxymoron. Capacity is not an exact thing like mass or volume but a stretchy think like a length of an elastic band. One can get much more out of the battery if he is willing to sacrifice longetivity and power. Different chemistry poses different price in longetivity when stretching capacity.

3. Model S is heavy and expensive. Tesla may use a a bit lower count of new cells to lower the weight and price of the pack. Lower weight will improve efficiency and driving feel.

4. Newer chemistry may be more susceptible to cycling and a biger unknown regarding lifetime so they may have chosen to reserve bigger part of 'total capacity' to meet lifetime goals.

5. Average annual capacity growth is a statistical observation in rear view mirror of las decade or two. It is not some hard fact to predict the future in a few years window. Real progress happens in litle steps, some smaller, other bigger. Using a new material in anode may open the door for another few years of a bit bigger steps and then again some amount of smaller ones when new capabilities of this new chemistries are pushed to its limits.
Interesting topic.
Is it possible that battery improvements are being made but that Tesla has been limiting the capacity? In other words, could the density of the batteries have been improving over recent years, but rather than extend range, they have been using less batteries?
Also, I'm sure it'd be nice to have more range, but perhaps they've found investing money in the Supercharger network (thereby making it easier to travel long distances this way) is more attractive to customers.
I know, that in theory, more range is better, however I see little complaining from people that own 85s that they need more range than they have. Believe Tesla has hit the sweet spot here on a Range vs Cost vs weight.

That is true for most of the days. However, a slightly larger battery would make a huge difference for those of us with real winters. I would have ordered that in a heartbeat.
We do know that the form factor and production facilities now used are similar to those that have been used since the Roadster. We also know that Roadster 3.0 has substantially increased capacity, although precise details have not been released (400 miles range IIRC is about the known information). Between a and D packs we can be assured there have been changes in connections, BMS and probably chemistry too. We also seem to know that the form factor will change when the Giga-Factory becomes operational. From all I have read it seems that is all we know.

Elon said on Friday that capacity has been increasing at about 5% per year, but did not say how, nor did he imply what increase in power density or capacity density resulted. He did say that the Ludicrous mode had been an unplanned consequence of the effort to develop 1,000,000 miles battery pack life.

Reading between the lines, I surmise that there are two related but distinct elements going on. 1) the so-called passive drain, (composed of BMS plus cell and wiring resistance), is being reduced; 2) the new fusing was designed originally for longer life, hence tighter BMS tolerances, giving the side benefit of tolerating at rise from 1300 amp max draw to 1500 amp max draw.

I therefore wager that we'll see slightly more than 5% per year improvement in buyable rated range, and upgrades will be available, at a price, for most Model S versions, if not all. The big unknown is what will happen with post Giga-Factory retrofits, assuming that a form factor change will also require complete rewiring and total change in the BMS.

Whatever happens, Model X will have as nearly equal range and performance as Tesla can achieve. Gotta beat all those AMG's and M's at a bare minimum, not to mention the dear departed LM 002 and the upcoming Bentley.
Is it too far-fetched to speculate that an X90 and X110 will be the offerings?
Marketing-wise (without overtly marketing, which after all is their way), the psychological reaction to 90 (Hmm, sounds incomplete) versus 110 (it goes to ELEVENTY) is pretty compelling to get the higher-spec option.

Probably is too soon for that stretch (though, I can't really believe in an X70).

Just musing.
If this is the 3600 mAh si anode cell, that would be a 6% improvement over the older 3400 mAh graphite one - in line with Elon's comment. This new electrode technology was first announced by Panasonic in 2009 and they are now running late.
There are various reports of opened packs but all found same count of cells.

Unless you check each cell for voltage you would not know. Some could be dummy cells.

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I was really surprised with the larger capacity battery being "only" 90kwh. That's hardly much of an improvement after 3-4 years. Given that the Model S is based on circa 2011/2012 battery technology and there have been annual improvements in battery technology Tesla likely could have released a 100kwh or greater battery pack if they wanted to. But the fact of the matter is they have no competition and they are likely holding back somewhat.

What would be interesting is if they had switched to the new chemistry months ago and simply replaced some of the cells with dummy cells, thereby "saving" batteries for more cars.