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Tesla Model S battery degradation data
61 points by dabeeeenster
https://steinbuch.wordpress.com/2015/01/24/tesla-model-s-battery...___________________________________________________________________
rodgerd - 28 minutes ago
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.
peterwwillis - 25 minutes ago
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.
sapienthomo - 2 minutes ago
The "technology" involved here is #1 understating the raw
capacity of the battery and #2 managing the charge/discharge
levels and rates to maintain that capacity. This gives a good
user experience and perception of longevity. Apple does the same
thing with the iPhone and it makes the iPhone user experience
noticeably better than comparable Android handsets where the
charge controller just charges the battery as high and as fast as
it can.Essentially, this is good UX, but for battery charge
indicators.
mschuster91 - 51 minutes ago
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 - 40 minutes ago
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?
mschuster91 - 33 minutes ago
You can replicate it to a certain extent by not discharging
below 10-20% (don't know the exact range though). Limiting
upper bound is likely either impossible or requires
reprogramming the battery control unit.What is also an
advantage: Teslas can cool (and I believe also heat) the
batteries so they don't enter temperature ranges where
degradation is accelerated. In a laptop and certainly a phone
there is neither space nor weight available for a thermal
management.
Zekio - 15 minutes ago
Pretty sure all newer thinkpads can be configured to only
charge to a threshold
cperciva - 30 minutes ago
I wonder if Tesla's battery technology could be used in laptops
and phones?Sure, if you want a laptop which you can only
recharge once per week.Laptops and phones go through charge
cycles much faster than cars; I'm sure Tesla has tuned their
designs to maximize performance in that usage environment.
fweespeech - 29 minutes ago
It's far less likely real technology and far more likely
massively undersold capacity in a Tesla.Laptop and phone
batteries are physically close to heat sources + are used
frequently to substantial degrees of discharge + frequency of
charge cycles after substantial discharge.
rcthompson - 29 minutes ago
I think the idea is if you programmed your laptop to never
charge the battery past 80% or discharge it past 20%, it would
degrade much more slowly, but you would also get about 40% less
battery life out of a single "full" charge. Or you would need
to increase the battery mass by 66% to get the same battery
life. Laptops need to be light enough for a human to carry,
while cars don't, and cars are generally expected to last
longer than laptops, so the second solution is probably more
viable for cars.
leggomylibro - 29 minutes ago
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.
[deleted]
xenadu02 - 11 minutes ago
I thought Tesla switched away from the laptop cells some time
ago?
r00fus - 33 minutes ago
The Prius did this - fanatically keep it's NiMH battery at
between 20 and 80% charge.I'm pretty sure cell phones do this
too.
[deleted]
dabeeeenster - 50 minutes ago
I think most/all EV's do this.
user5994461 - 50 minutes ago
They do it to different degrees.
vvanders - 48 minutes ago
Yup and that's totally fine in my book since they're selling a
rated range.My single datapoint at 60k is I've seen only 2%
degradation which is phenomenal.
obblekk - 49 minutes ago
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 - 12 minutes ago
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.
TomMarius - 47 minutes ago
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.
IkmoIkmo - 31 minutes ago
> Average life of ICE vehicles can't be 266kkm, that's absurdly
low.I'm not sure it is...I mean, in my country (Netherlands) the
average car user drives 13k km per year, in very car heavy
countries that's probably around 20k. But here it'd mean a car
would last on average 20 years, that's not absurdly low by any
standard.
TomMarius - 24 minutes ago
OK, maybe I misunderstood. To me it seems like it's comparation
of incomparable though - you can't fault the vehicle that you
didn't use it enough to broke it and had its life ended just
because of age. With proper care, the vehicle could go much
farther than 500k km with no noticeable performance or range
degradations - just like the heavily used Teslas.
sorenjan - 29 minutes ago
I've never seen anyone put more than one kilo before the unit
before.
dom0 - 24 minutes ago
Well Americans did (sometimes still do) use micro-micro, as in
??F.
TomMarius - 21 minutes ago
For me, it's normal to write "its mileage is 165k" - and the
"km" is assumed. I just wanted our friends that use imperial
units to understand, you're true it's non-standard, and it's
actually the first time I wrote it like that.
sqeaky - 40 minutes ago
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.
vvanders - 37 minutes ago
Yup, when I donated my car at 145k mi I expected to to be
resold but got notified that it was turned into parts for
$350(they had to report back to me for tax reasons).
dom0 - 32 minutes ago
97 000 miles, just barely 160k kilometers. That's... really not
much at all.
seszett - 31 minutes ago
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 - 23 minutes ago
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.
nathancahill - 14 minutes ago
Huh, I drive a Toyota with 205,000 miles on it. Still in
great condition after tons of cross-country road trips.
Animats - 14 minutes ago
I'm up to 235,000 miles on a 1985 Ford Bronco as the
original owner, but that's a 2-ton truck. High-mileage
trucks aren't that unusual.
apapli - 11 minutes ago
We had a (1988?) family Peugeot 505 station wagon that made
over 600,000kms back in the day.Perhaps they don't build
them like they used to, but our 1980's Honda sedan also
easily clicked over 350,000kms too.
seszett - 6 minutes ago
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.
TomMarius - 31 minutes ago
Uhh... My own car has around 98k miles (165kkm) and I consider
it pretty new.
kbenson - 43 minutes ago
> 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=149700022:
https://news.ycombinator.com/item?id=14862695
microcolonel - 1 minutes ago
Frankly it might be a bit confusing to Canadians.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?
dmitrygr - 40 minutes ago
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/scienc
e/article/pii/S0378775316...
colechristensen - 38 minutes ago
Lithium batteries lose charge with use as well. Also rate of
charge/discharge. It's more complicated than just one thing.
epistasis - 37 minutes ago
Wow, I've never heard anybody say that before or model it that
way before.Though these tests are evidence of that, it's
definitely not a common belief.Before the Tesla data, what
informed you?
JshWright - 34 minutes ago
In the RC world, the '50/50' rule of thumb is common for
lithium battery storage. 50% charge at 50?F. It's close enough
to the 'ideal' values, and easy to remember (for those of us
used to a human-centric temperature scale)
dom0 - 15 minutes ago
> human-centric temperature scaleOne point (100 ?F ~ 37 ?C)
doesn't make a scale.
JshWright - 2 minutes ago
Heh, sorry, that was just a tongue-in-cheek joke, not a
central point of my comment.0 to 100 on the Fahrenheit
scale is "Really Cold" to "Really Hot".0 to 100 on the
Celsius scale is "Kinda Cold" to "Unsurvivable Hot".When I
say it's "human-centric" I mean that it maps well to the
range of human comfort (Celsius is obviously vastly
superior in just about every other use).
dmitrygr - 32 minutes ago
I provided a citation. Feel free to google around to find more
info. This is basically how everyone models LiPo and Li-Ion
cells. Tesla only publishes marketingspeak (which makes sense -
that makes them money). Look for actual science and you'll see
epistasis - 23 minutes ago
Weird, was that there when I replied? I definitely don't
remember seeing it there... Perhaps I was just rushed.In any
case thanks for the source!
vvanders - 34 minutes ago
Phone batteries do poorly because the SoC generates a ton of heat
when used which gets dumped right on the battery pouch.It's the
same reason that you see early Leaf cells die out in Arizona
while Tesla's have held up to 100k+. Thermal management makes or
breaks longevity.
dmitrygr - 33 minutes ago
yes... I said that...high temp is bad
tertius - 30 minutes ago
To be fair for phones you focused on: 100% charge and pocket
(body) heat.You did mention 100% and temperature being the
problem generally though...
vvanders - 26 minutes ago
Sure, but you lead with:> not because of amount of use, but
because of timeWhich makes it seem like time is more
important that heat.
dmitrygr - 20 minutes ago
heat != usethink of it more asBADNESS = integral(abs(temp -
5), over time) * integral(abs(charge_amt - 40%), over time)
zecken - 30 minutes ago
It seems like the opposite might be true, and that batteries
degrade from cycle count and not because of time. This is why
they are rated in cycle counts (i.e. cycles until 80% capacity =
life time of battery). Also important is the charge/discharge
rate, but because the batteries are so oversized in Teslas they
can discharge as low as .25C even at highway speeds which helps
increase their lifetime.source:
http://batteryuniversity.com/learn/article/what_causes_lithi...
dmitrygr - 29 minutes ago
They are rated in cycles so consumers do not need a degree in
physics to understand the reality. Feel free to inspect a REAL
spec sheet for a LiPo battery from a manufacturer (I think ATL
provides some online)
sqeaky - 27 minutes ago
Can you provide links? You clearly feel we have never seen a
"real" sheet, perhaps more hand holding is order. I would
appreciate the experience and would not do it without the
link.
dmitrygr - 18 minutes ago
I am trying to find some non-NDA specs online for you. I
saw this when I was working with these for a job and the
specsheet was NDA (and I no longer work at the place this
was)
hwillis - moments ago
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.