
Tesla Model S battery degradation data - dabeeeenster
https://steinbuch.wordpress.com/2015/01/24/tesla-model-s-battery-degradation-data/
======
jakobegger
Doesn‘t anybody find it curious that the source of data are range estimates
displayed on the cars built-in dashboard?

For all we know, Teslas might be programmed to show more „optimistic“
estimates as the batteries get older.

I‘m not saying this is actually the case, but these stats are effectively
manufacturer-provided numbers. Would you trust data like this if it came from
any other car manufacturer?

If you have a gasoline car, do you trust the fuel consumption rate displayed
on the dashboard? Should journalists trust it? Or should they measure how much
gas they put in the tank and divide it by distance driven?

~~~
dcustodio
I fill up every time I refuel and I take notes of the quantity and odometer
and the average matches the dashboard.

~~~
72deluxe
What manufacturer and model is that?

I had a 2008 VW Golf TDI Gt Sport (the 140PS PD engine) and that consistently
lied. My newer 150 Euro6 (I think) engined VW Beetle TDO gives even better MPG
so perhaps it is lying again... Potentially time to measure it versus how much
I put in.

~~~
Tepix
How do you measure the distance driven? Perhaps the tachometer is also lying?

~~~
freehunter
Very good point. Odometers (tachometer measures RPM, odometer measures
distance) are not as reliable as some may believe, and even if they're
perfectly accurate, there are so many variables that it's hard to control.
Smaller tires spin faster, which drives up the miles read. Tires get smaller
as they wear, so the odometer can be calibrated for new tires but will quickly
become inaccurate.

But the odds that your odometer is accurate is very slim in reality:
[http://www.azfamily.com/story/19769079/tests-show-
odometers-...](http://www.azfamily.com/story/19769079/tests-show-odometers-
inaccurate-regardless-of-make-model)

------
kbenson
> The red fitted line has a slope above 60.000 km (say 40,000 miles) of 1% per
> 50.000 km (30,000 miles).

I'm going to bring this up because I think it's both interesting, and
sometimes it comes up on its own and detracts from the conversation with
conjecture (and sometimes harsh assumptions) until covered adequately[1] -
different countries have different conventions for whether they use a comma or
period for a thousands separator, and in those languages if they _also_ speak
in English sometimes, they may choose to continue using a period as a
thousands separator as is convention in their country, even if the predominant
language in their country is not English, and there are circumstances which
might make that more common for some people.[2]

In this case, we have what appears to be switching convention when switching
unit systems, which is interesting. I'm not sure if it's more or less
confusing in the end, but there's not really any standardization of this as
far as I know, so it's all good.

1:
[https://news.ycombinator.com/item?id=14970002](https://news.ycombinator.com/item?id=14970002)

2:
[https://news.ycombinator.com/item?id=14862695](https://news.ycombinator.com/item?id=14862695)

~~~
microcolonel
Frankly it might be a bit confusing to Canadians, here we use the U.S. numeric
conventions, but we tend to use a mix of SI and imperial units, and in this
case we'd use kilometres for ground distance, with thousands separated by
commas. The UK also seems to prefer commas to separate thousands.

I'm inoculated against confusion about this because I've done a lot of
software and content localization, and have a grasp on the specifics for a lot
of different cultures.

I think the problem is exacerbated by the underuse of the SI system's
prefixes. Why even talk about thousands of kilometres when you can speak in
tens of megametres?

 _Added:_

I figure it's getting to the point where there are too many genuine English
locales to keep up. It takes a lot of energy for normal people to retain
fluency in dialects and locales like en_US, en_IN, en_CA (thankfully rapidly
merging with en_US), en_GB, en_AU, en_JM, en_MY, etc. etc. etc.. all at the
same time. Maybe at some point there will be a great and natural convergence.

~~~
photojosh
> Why even talk about thousands of kilometres when you can speak in tens of
> megametres?

Probably because when you're speaking about them colloquially, you don't say
"kilometres" you say "kays". That probably varies by locale too, I'm in en_AU.
How is it over your way?

I do like the nerdiness in the idea of saying "two megs" instead of "two
thousand kays", but it's never going to happen.

~~~
Coincoin
>I do like the nerdiness in the idea of saying "two megs" instead of "two
thousand kays"

But they are not the same!!oneoneone. Unless you are in the dog food prefixes
camp. Are you?

~~~
photojosh
2 000 km = 2 Mm?

You're not thinking of the mebi-, kibi-, etc debacle, are you?

~~~
Coincoin
Yes. I'm old school, 1K is 1024, 1M is 1024K, 64K is 65536 and I refuse to use
kimblebits and such.

Ah... screw it: [https://www.xkcd.com/394/](https://www.xkcd.com/394/)

~~~
photojosh
I'm with you, but it's a non-issue when it comes to non-computer units, which
is what we're discussing here.

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GuB-42
That's quite impressive. What I am wondering is why they do do well, barely
losing 10% in 5 years, compared to phone or laptop batteries that last maybe 3
years on average. AFAIK, they use the same technology, in fact, I wouldn't be
surprised if the same batch of cells end up partly in Teslas and partly in
laptops.

~~~
hwillis
In order of importance:

1: Tesla cells are hard limited to a lower voltage, reportedly 4.1 V rather
than the 4.2-4.4 V maximum. Phone batteries run much closer to their maximum
voltage

2: Tesla cells stay at much lower temperatures and have active cooling. Phone
batteries are used to _sink_ heat from the processors and wifi.

3: Teslas have a much lower normal depth of discharge. In addition to the
derated voltage, the average American's daily driving distance is ~30 miles or
10-15% of the battery capacity. Phones are often almost totally discharged
every day. Tesla's are also typically only charged to 80%, although you can
turn that off.

4: Teslas have a low average power use: 300-600 horsepower on tap but cruising
on the highway uses very little. In technical terms their current rate is
~.2-.3 C, while phones can have much higher C rates.

5: Phones use an LCO chemistry, Teslas use NCA which is more stable over the
long term. Tesla also has custom additive and cathode/anode materials that
improve lifespan a great deal.

Phone and laptop batteries almost all come from china, Tesla batteries are
korean. They're pretty premium as far as 18650s go so they're used in power
tools and really good laptops. However Tesla has their own proprietary
chemistry so nobody else gets to use their blend.

~~~
digikata
A lot of these could be mitigated if phone makers were willing to put in a
slightly larger capacity battery and apply more conservative max-min limits in
their battery management system. But I guess companies are happy to keep sales
up via planned obsolescence.

~~~
photojosh
My phone rarely gets below 50%, and I'd say it only gets below 20% a handful
of days a year.

But yes, I've often thought it would be nice to have a toggle to say "Prolong
battery life (as in years)... I only want a 90% charge since I'm not going to
be using much tomorrow."

I've wondered too whether I should only use a slow (1A) charger for the
overnight charge rather than the full 2.4A. But then again, I only keep my
phone for 2 years before passing on it, so I've not had to care that much.

~~~
lorenzhs
I know ThinkPad laptops have this (mine is set to charge up to 90% and only
start charging if it's below 80%), and I think I've seen it in some custom
kernels for Android ROMs a few years ago, but I'm not aware of any popular
devices supporting something like this.

~~~
gambiting
Sony phones have that, I have an Xperia Z5 and you can select an option to
"prelong battery life", where the phone only charges it up to 80% and
stops(the scale shifts, so 80% shows as 100%, but internally the battery is
never at 100%).

------
11thEarlOfMar
This is pretty surprising. What it means is that most owners will not need to
replace their batteries in the time that they own the car. In my 'total cost
of ownership' models, I've assumed a battery replacement at 100,000 miles, but
that appears to not be necessary. This changes the calculation considerably.
Not to mention that if the drive train can go 400,000 miles without needing
major repair, I can keep the car 2x as long as an ICE, further reducing the
cost of owning an electric vehicle.

~~~
toomuchtodo
Musk has made a comment on an investor call that they're targeting a million
mile lifespan for the motor.

~~~
dalbasal
I think ICE cars are just not optimized for prolonged life. Many countries
have policies discouraging long lifespans, more than ever since emmissions
laws. Also, EOL for a car is several owners and 5-10 years removed from first
purchase.

This adds up to a realtiy where doubling the expected lifespan is not worth
much more, in sales.

Basically, if Tesla want to make this a goal then beating benchmarks should be
relatively easy.

~~~
dsfyu404ed
x2. Modern vehicles have a targeted minimum lifetime based on certain usage
models. That's why people who are driving a pickup truck around all day for
work with a few hundred pounds of equipment (e.g. medical equipment service
technician) get 500k+ out of them and oil field trucks are beat before 100k.

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dmitrygr
This is fundamentally flawed because lithium batteries mostly degrade not
because of amount of use, but because of time (and their charge state and
temperature during this time). No matter if used or not, they will lose
capacity. The rate of capacity loss is mainly dependent of average charge
(best is 40%, worst is 100%) and temperature (best is 5 degrees C, the higher
the worse).

(This is also why phone batteries fare so badly: they are often near 100%
charge at 36.6 C in your pocket)

[http://www.sciencedirect.com/science/article/pii/S0378775316...](http://www.sciencedirect.com/science/article/pii/S0378775316316998)

~~~
WillPostForFood
So if you were optimizing your phone for low battery degradation, when would
you charge it, and to what %? If you were trying to keep it around 40%, would
a good strategy be to let drop to 20%, and then only charge to 60%, or would
you bias it even lower to keep it away from 100%, like a working range of
10-50%?

~~~
skykooler
The ideal state of charge for a lithium battery is 50%. So charging between
20% and 80% would significantly lengthen battery life. If you wanted to
completely optimize for low battery degradation you'd charge between like 49%
and 51% and only have a few minutes of usage, but that kind of defeats the
point of keeping a lot of battery capacity.

------
RoboTeddy
Battery science is fascinating. Here's in an-depth look at degredation:
[https://www.youtube.com/watch?v=9qi03QawZEk](https://www.youtube.com/watch?v=9qi03QawZEk)

The speaker (Jeff Dahn -- he now works with Tesla) pioneered a faster way to
tell how fast a battery will degrade (which means you can iterate your design
faster!)

------
mschuster91
What could explain the graphs and cycle stability is that Tesla does not
deplete the battery pack below a certain percentage of the real battery
capacity or over a threshold... basically they keep the battery pack well
beyond the critical ranges where batteries degrade from simply idling, and
they "undersell" the pack capacity.

~~~
RachelF
I've always wondered how they do it.

They use the same 18650 cells that power laptops, yet laptop batteries degrade
badly over time. My 1 year old XPS13 reports a battery "wear level" of 29%.

I wonder if Tesla's battery technology could be used in laptops and phones?

~~~
leggomylibro
I wonder if they're particularly good at balancing the cells. When people
recycle 18650s from laptops, I think it's often because one or two cells went
bad while the rest remain fairly healthy.

Similarly, if you put things like batteries or capacitors in series, you
typically want circuitry to balance their voltages, because a pair of 2.7V
elements charged to 5.3V could really be at say, 2.75V and 2.55V, which would
be unhealthy for the former cell. I think those imbalances are also caused by
small differences in the individual elements' properties (capacitors are
typically less precisely-tuned than resistors) which will drift further over
time with wear and temperature changes and overvoltage conditions and whatnot.
So that 2.75V cell would degrade very rapidly compared to the 2.55V one,
probably causing even larger imbalances until it eventually fails.

Most lithium cells have basic protection circuits built-in against over/under
voltage and overcurrent (e.g. shorts,) because they tend to explode if you
leave those things out, but they definitely last longer if you pay attention
to them as individual cells rather than a system.

~~~
Meegul
A Tesla focused Youtuber recently did a video [1] where he accessed some of
the data on the CAN bus, and it showed _excellent_ balancing between the
cells. The highest voltage cell reported 3.87V, with the lowest voltage cell
reporting 3.864V. So the highest voltage cell has only a 0.1% higher voltage
than the lowest. That's in the middle of a discharge cycle, so this may not be
representative of the real capacity difference of each cell, but they're being
discharging in a very balanced manner. I don't work with batteries often, so
take my analysis with a grain of salt, but it seems to me that (the lack of)
battery degradation is one of Tesla's biggest strengths when it comes to their
battery technology.

1 - [https://youtu.be/F3tF0i98MpI](https://youtu.be/F3tF0i98MpI)

~~~
jakobegger
Presumably they have a lot of cells in parallel? This would help with
balancing, since individual cell differences would average out over all the
cells that are parallel.

------
TomMarius
Average life of ICE vehicles can't be 266kkm, that's absurdly low. Most of
people I know have _bought_ vehicles with that mileage and used it for another
100kkm after that at some point in their life (think first/second car, second
family car, etc.). It's important to know that especially in Central/Eastern
Europe, you can _never_ trust the car's odometer - even the cars I'm talking
about had probably more than 350kkm when bought.

~~~
sqeaky
I have seen plenty of cars not make to 165_000 miles, those that do are often
near the end of their life. Mine is beat and barely holding together and it is
at 97_000 miles.

~~~
seszett
165 000 miles is 266 000 km, for the readers who might wonder.

My car is at 350 000 km now, and I'm not planning on selling it anytime soon.
It doesn't have any special problem, except for a malfunctioning electric
window lifter on one side. It's only one data point of course.

~~~
sqeaky
What percentage of car owners do this?

There is some percentage of cars crashed in the first week. It only takes a
few of these to cancel out the average of extreme outliers like your car.

For reference I have never seen an odometer with more than 200 000 on it
before. Even most classic rebuilds I have seen like 69 Corvettes have some
high 100K count on them, some event have reset odometers.

~~~
seszett
I don't know, but if the average is 220 000 km (according to the article) I'd
say a fair share of cars must go beyond that.

If I had not bought my car (it was at 300 000 km) I'm pretty sure it would
have been sold in Eastern Europe instead, or maybe Africa since it's a Peugeot
(a 406).

In the countryside, it's also very common to have both a nice recent car, and
an old reliable one like mine for the dirty work. Most people I know do have
one car that is a few 100 000s of km. Also, we mostly use diesel here, and
these are supposed to be much more reliable than the gasoline engines used in
the US (and I'm not going into the purported lack of reliability of American
cars to begin with). I'm talking about everyday cars that are 15 or 20 years
old, not classic cars.

~~~
dom0
Gasoline engines can be plenty reliable. I think the main reason why a lot of
cars from the 80s and 90s are able to go to 400k and more is (1) cheaper and
easier maintenance, so more inclined to do it regularly (2) no fancy shit
going on, no turbo chargers, no high-pressure fuel injection, thus far less
wear on parts, no unreliable high-pressure pumps etc.

Replacement parts on these are also far more expensive. New turbo is a four-
figure number just for the part. Injection pumps are bloody expensive, too.

Less optimized designs may also be a factor. CAD and FEM modelling has only
become better with time, so back in the day engineers would rather make a more
conservative design, nowadays that's not so necessary any more.

~~~
tyingq
Aluminum heads are part of why some newer cars don't last as long. It's easier
to blow a head gasket. Replacing those in a tightly packed front wheel drive
engine bay often exceeds the value of the car. Or, driving with the blown
gasket causes overheating that damages other components.

------
hwillis
You lose about 5% capacity in the first 45k miles, then it's essentially flat-
3% in 120k miles. It seems like keeping your charge level at 100% has some
impact on lifetime, but lower than 90% looks to have very limited returns.
I'll be interested to see how the cycle graph evolves, but right now it looks
like batteries will on average make it to 2500-3000 cycles, which is great.

There are a number of early outliers that had more significant capacity loss.
They're all from the US- Europe & Asia have over 800 reports compared to 170
in the US, but the lowest reading there is 88% compared to 85% in the US. All
with ~<35k miles, <4 years old, mostly 60 kWh models. I'm not quite ready to
call fake, but the numbers from the US are definitely unlike other countries.

Those cars weren't driven nearly as hard as their counterparts in other
countries. The only real explanation other than false reporting is heat, but
unfortunately there is no indication of location besides one guy in Michigan.
Keep that in mind when looking at all the graphs- the lowest data points are
almost exclusively very strange outliers from the US that weren't driven
particularly hard.

~~~
ProfessorLayton
IIRC no high voltage car batteries are actually charged/discharged 0-100%,
even if it reads so from the user's perspective. This is due to significantly
increased wear on the batteries when fully charged/discharged, and why a
cellphone battery only lasts a few years.

The batteries need to be significantly over-provisioned to extend their
lifespan. A Prius, for example, will keep the battery's SOC between 40-80%,
and is one of the most reliable hybrids out there.

The same is true for EVs, so charging it till it reads 100% does not mean the
battery is at capacity. The same is true when it reads empty.

~~~
mikeash
I don't think any lithium ion battery is ever truly used at 0-100%. True 100%
would be just before it explodes, and true 0% would be just before it
completely bricks. You get horrible degradation near those areas so they're
always avoided. I'm sure consumer electronics push it farther than cars do,
though.

------
peterwwillis
FYI: Tesla batteries are literally laptop batteries with cell balancing. No
secret battery magic going on.

You could in theory crack open the pack and replace inefficient cells to get
your capacity back. But, I'm assuming this is too huge a PITA for most people.

~~~
fish_fan
I thought laptop batteries are also a bunch of phone batteries stuck together.
Is that assumption incorrect?

Edit: apparently so.... I would appreciate a reply if anyone has time. I have
a difficult time figuring out what about my question could have caused
disagreement.

~~~
abawany
Not an expert and I didn't downvote but from my examination of laptop
batteries, they appear to be composed of LIon cells of a standard size,
something like 3V cells. Phone batteries OTOH seem to be pretty custom designs
to fit a specific phone or range of phones. For e.g.
[https://electronics.stackexchange.com/questions/156928/repla...](https://electronics.stackexchange.com/questions/156928/replacing-18650-cells-
in-laptop-battery-with-greater-capacity-ones)

Edit: added link.

------
rodgerd
Presenting the Telsa graph with the full x axis (to demonstrate the rate of
degradation is very small), and then the Leaf with a reduced x axis (to
suggest it's got serious problems) doesn't really lend confidence.

------
friendzis
There is one thing about batteries: Watt-hours battery will provide highly
depend on current (electric current) draw. To some extent this also applies to
deterioration. Which means that as batteries get more and more used, one
should expect to see higher and higher disparity between range in sporty and
economic driving. In other words as battery gets older, the higher consumption
driving aggressively.

Tesla, however, has one redeeming factor. While battery voltage-
capacity@current curve will change over time, Tesla can collect real world
usage data and with software updates push updated curves for older batteries
to adjust range estimation models for battery wear.

------
amgin3
If it were the same quality as my laptop battery, you would have to keep it
plugged in while driving after 1 year.

------
iambateman
Correct me if I'm wrong, but Lithium Ion batteries have exponential
degradation, right?

The data here assumes constant degradation, which is going to throw this off.

------
lafar6502
What all these dots above 100% mean, besides moving the average up? And I'd be
worried about the owners of all these dots below the line

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redthrowaway
>Want to buy a Tesla? Use my referral link!

Man, this only needs to work once for it to easily outstrip all other forms of
revenue a blog might generate.

~~~
sowbug
The current referral program offers only non-monetary awards (toy car, fancy
wheels, entry in contest to win car). Better than a poke in the eye, but not
as good as cash.

~~~
incompatible
There's not much point in Tesla offering a lot. A search for "Tesla" in Google
gets you to the right place to buy one with a couple of clicks.

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obblekk
Is there a non-linear decline at the end? i.e. do the batteries at some point
just give up and capacity starts declining very quickly?

~~~
tinus_hn
In the comments it is explained that this is because there is only one user
who made it that far so the graph is skewed towards that users data. That
users battery happened to be slightly worse than the mean so the graph goes
down. It doesn't really mean anything.

------
lafar6502
So you can conclude your car willl be worth nothing after 200k miles

------
bunkydoo
I'm just over here patiently awaiting some startup to unseat Tesla as the king
of speedy, luxury, electric automotive. Nobody is quite taking the cake, or
even trying for that matter.

~~~
hwillis
There are at least a dozen companies trying to do exactly that. Thing is,
Tesla was _exceptionally_ lucky, and it is still incredibly hard to build a
car company. Tesla managed to squeak through to the Model S, which was
absolutely critical.

For companies that are trying to make a Tesla killer, they have to hit the
price point above a Model S with zero volume. That's means no factory and hand
building almost everything. That destroys any ability to price reasonably.
Tesla killers start at 300k and range up to 2 million. Nobody at that price
point wants electric cars right now, or at least very few people. It doesn't
come with the same bragging rights as a Ferrari or Koenigsegg. Those have
brand and absolute, vastly supreme performance respectively.

Also, I suspect people are aware that as soon as Tesla announces a new
roadster the game will be over. Nobody will want to buy anything else.

