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What does the battery degradation curve look like?

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pguerra

Member
Oct 22, 2011
180
1
#1
The recent German article that reports that one owner's Roadster is getting only 100 km of range after going 150k miles is highly concerning for me.

Cinergi's Roadster over a 2 year period driving a total of 20k miles decreased from 188 miles to 181 miles in range (standard charging). This is about a 4% decrease (or 2% / year or 1% / 5k miles, etc). My opinion is that this rate is a moderate amount.

My question is if anyone knows the answer:

What does the battery degradation curve look like? 1, 2, or 3 below? I.e. is battery degradation linear or "curvilinear" (I think that's the term?)?
Graph battery degradation.jpg
(If I had to guess, I guess it would be number 3).

I'm sure enough research has been done that one can estimate range after X amount of driving with average charging habits. Even if basing off Roadster doesn't exactly apply to Model S due to different technology, I'd still like to try to know what kind of range I can expect after say 50k and 100k miles. I prefer answers that are realistic and not Tesla hype, sugar-coated, or "best case" scenarios.

Thanks in advance.
 
#2
My Roadster's age and mileage are very similar to Cinergi's, and the degradation rate is pretty much the same.

I don't have any data to support this, but if I had to guess the decline will be straight-line for a long time, and then towards the end of life it would speed up. That's because you have to use a greater percentage of the remaining battery capacity to achieve the same range.

I expect my pack to last a good long time.
 
#4
And according to this article about lithium technology the Roadster battery has a life span rating of 3/5, and the Model S battery as a life span rating of 5/5.
Types of Lithium-ion Batteries – Battery University

Not sure what this translates to, but it`s obvious that Model S batteries will suffer from less degradation from wear/age. If 50.000 miles and 4 years result in 10% degradation of the Roadster battery, then the Model S might get 5-6 years and 60-80.000 miles before reaching 10% loss?

Edit: anyone want to buy a report exploring NCA degradation? :) http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=6043110&url=http%3A%2F%2Fieeexplore.ieee.org%2Fxpls%2Fabs_all.jsp%3Farnumber%3D6043110

Second edit: Quote: "on the other hand, NCA has much better cycle life." http://www.neicorporation.com/white-papers/Lithium-titanate-LTO_Anode_high-rate-cycle-life-batteries.pdf
Not quantified though.
 
Last edited:
#5
donauker said:
At 3.5 years and 48K miles I get 169 standard mode miles so about a 10% loss.
Click to expand...

Since it seems that Roadsters are having similar degradation rates, would it be okay to extrapolate and say that at 100k odometer miles, a Roadster would have roughly a 20% loss of range? And a 30% loss of range at 150k? (Yes, all rough estimates).

Further, since battery technology (Thank you for those links, Oyvind.H!) in the Model S is supposedly better than in the Roadster, that I should expect LESS than a 10% loss of range in the Model S at 50k odometer miles?

So since battery degradation is real and inevitable after how many miles or years of driving Model S will I have to FOR SURE replace the battery b/c it is no longer holding an adequate enough charge? 8 years? 10 yrs? Does this sound about right?

Thank you.
 
#6
pguerra said:
So since battery degradation is real and inevitable after how many miles or years of driving Model S will I have to FOR SURE replace the battery b/c it is no longer holding an adequate enough charge?
Click to expand...

That depends on your requirements. I'm buying the 85kWh battery pack; if I'm only using it to buy groceries in 10 years time then I'll be happy if I'm getting 50 miles per charge, OTOH if I'm doing an 80 miles roundtrip daily commute and I can't get 100 miles on a charge that would be a problem.
 
#8
I posted this in the other thread, but it is perhaps more relevent here.

If you want to drive exactly 145 miles per day, every day for 1035 days, you will hit 150,000 miles ( 241,400 km ).

If the battery degrades linearly to 70% original capacity by the 100,000 mile mark, your max range will hit 189 miles after 488 days and 71920 miles.
189 miles max range mode will be 145 miles in standard mode ( assuming standard charges to 87% of range mode, and hides the bottom 10% ).
If you aren't comfortable in standard mode, and start charging in range mode at that point, that means that for the next 547 days you will charge in range mode, which is a lot.
If you wait until standard mode ( including the hidden 10% ) is 145 miles, that would be at max range of 167 miles - which would happen at 697 days and 101065 miles. That means for the next 338 days you will charge in range mode every day.

At 905 days and 131225 miles your max range will drop to 145 miles and you will no longer be able to drive 145 miles on one charge. However I bet that charging every day in range mode after 100,000 miles will make the range drop faster than it was for the first 100,000.

My conclusion:
To get to 150,000 miles in about 3 years, you very likely do a HUGE AMOUNT of range mode charging. This almost certainly shortens the life of the battery. You might not, you might charge multiple times every day, and get your mileage in without range mode charging at all.

You could easily get to 150,000 miles in 10 years and never do a range mode charge, and it is very likely your battery will perform better.
 
#9
pguerra said:
Since it seems that Roadsters are having similar degradation rates, would it be okay to extrapolate and say that at 100k odometer miles, a Roadster would have roughly a 20% loss of range? And a 30% loss of range at 150k? (Yes, all rough estimates).

Further, since battery technology (Thank you for those links, Oyvind.H!) in the Model S is supposedly better than in the Roadster, that I should expect LESS than a 10% loss of range in the Model S at 50k odometer miles?

So since battery degradation is real and inevitable after how many miles or years of driving Model S will I have to FOR SURE replace the battery b/c it is no longer holding an adequate enough charge? 8 years? 10 yrs? Does this sound about right?

Thank you.
Click to expand...

Also take into account how deeply you cycle the batteries. Similar driving habits on a 40kWh pack will cycle it more, a 60kWh pack will cycle about the same number of times as a roadster, while the 85kWh pack will cycle less (half as much as a 40kWh pack). So the 85kWh will survive miles better than the other two and degrade less. The time degradation is probably going to be constant across all the packs.

This as on major reason why I upgraded to the 85kWh pack, I am no longer afraid of degradation during the life of the rest of the car, or have to plan on replacing a battery pack.
 
#10
ElSupreme said:
Also take into account how deeply you cycle the batteries. Similar driving habits on a 40kWh pack will cycle it more, a 60kWh pack will cycle about the same number of times as a roadster, while the 85kWh pack will cycle less (half as much as a 40kWh pack). So the 85kWh will survive miles better than the other two and degrade less. The time degradation is probably going to be constant across all the packs.

This as on major reason why I upgraded to the 85kWh pack, I am no longer afraid of degradation during the life of the rest of the car, or have to plan on replacing a battery pack.
Click to expand...

Man I hope you're right, and it does seem to make sense to me. I called Tesla to ask more, and the "answer" was that "it's all theory" and battery degradation rate wasn't known (though they said it was 4-7% in the Roadster). But the person I spoke with said that he thinks if he can recall correctly:

1) battery degradation is like the curve in number three above
2) "72%" was max that the battery degrades and then it remains there "for a decade". The asymptote if you will (whoa, I've NEVER used that word in a real sentence before!).

If this is true, then you can take roughly a third of the max range at maximal battery degradation or 265 mi X 0.33 = 178 miles max range.

Also, if it is true that battery technology is better than the Roadster, then getting to the batteries maximal degradation should take longer than in the Roadster. So, just a guess, maybe my Model S battery will degrade maximally in 5-8 yrs.

Finally, I do remember something about battery tech improving 4-8% / yr. So conceivably, same type battery could be purchased for that much cheaper for each year that goes by.

Bottom line: I guess it'll be okay, and I shouldn't cancel my reservation, lose 10k, and lease a Volt to make sure all the quirks have been ironed out in Model S.
 
#11
Tesla is very unlikely to pass along battery savings onto the consumer for a few years. They'll just increase their margins and keep the prices the same (Apple does this with the new iPad costing the same as the last version but with better specs).

Battery tech will improve with each year but like computers, if you keep waiting for the next big thing you'll never buy anything. If it really does level off like that then that's great. I think most people will either buy a new car in 10 years or upgrade the battery at that point but some people do keep cars for 10-20 years or more.
 
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#12
richkae said:
I posted this in the other thread, but it is perhaps more relevent here.

If you want to drive exactly 145 miles per day, every day for 1035 days, you will hit 150,000 miles ( 241,400 km ).

If the battery degrades linearly to 70% original capacity by the 100,000 mile mark, your max range will hit 189 miles after 488 days and 71920 miles.
189 miles max range mode will be 145 miles in standard mode ( assuming standard charges to 87% of range mode, and hides the bottom 10% ).
If you aren't comfortable in standard mode, and start charging in range mode at that point, that means that for the next 547 days you will charge in range mode, which is a lot.
If you wait until standard mode ( including the hidden 10% ) is 145 miles, that would be at max range of 167 miles - which would happen at 697 days and 101065 miles. That means for the next 338 days you will charge in range mode every day.

At 905 days and 131225 miles your max range will drop to 145 miles and you will no longer be able to drive 145 miles on one charge. However I bet that charging every day in range mode after 100,000 miles will make the range drop faster than it was for the first 100,000.

My conclusion:
To get to 150,000 miles in about 3 years, you very likely do a HUGE AMOUNT of range mode charging. This almost certainly shortens the life of the battery. You might not, you might charge multiple times every day, and get your mileage in without range mode charging at all.

You could easily get to 150,000 miles in 10 years and never do a range mode charge, and it is very likely your battery will perform better.
Click to expand...

Unlike the Roadster, the Model S does not hide the bottom 10% of charge in Standard mode. How does that affect your analysis?
 
#13
dsm363 said:
Battery tech will improve with each year but like computers, if you keep waiting for the next big thing you'll never buy anything.
Click to expand...
Actually, major breakthroughs will cause energy storage tech to improve suddenly and massively. I know of one. :) Unfortunately the difficulties of commercialization and mass production will probably prevent this from making it into cars for 10 years or more. So unless you're planning to keep your car for longer than that....
 
#14
@neroden: I agree that there are several interesting battery techs in the lab -- I'm always glad to hear that there are some as-yet unreleased techs, too. I also agree with your assessment that the time between the "ah ha!" proof of viability and when factories are turning out volumes of automotive-grade cells using that technology is substantial. I'm looking forward to having the 2022 replacement battery in my 2012 Model S be something amazing -- lighter, cheaper, and higher capacity.

Battery improvements need not be continuous; when people say "8%/year", I think it's even more likely that in any given year the improvement is much smaller, but once in a while we get a big step-change up.
 
#15
I would like offer an expert comment on the issue of the life of the Model S battery. I am a Model S reservation holder and also lithium ion battery expert. In my most recent battery assignment I lead over a 10 year period the qualification of a Li/NCA system for used very expensive autonomous satellites. This effort succeeded through a combination of careful life testing, detailed analysis of test articles and development of a heuristic model based on quantum mechanics which provides a high confidence prediction of operation life.
To answer the question which kicked on this thread battery degradation with time basically follows Pguerra case 3 as illustrated below with experimental and theoretical data for a real NCA system.

Picture1.png


While I have not worked with the Panasonic NCA system I believe my experience is close enough to provide some useful rules of thumb. First, all degradation process are a function of applied stress. Three common stresses that a battery sees are temperature (the Tesla battery is water cooled for a reason), voltage (the maximum mileage you charge the battery to) and depth of discharge (miles per day, note this is why the only 85 kWh variant has an year warrantee).
I have employed my battery models to predict Model S life and the results are outstanding. I believe that if routine charging is limited to about 80% of maximum mileage (~200 miles) and average daily use to 60 to 70 miles (my present commute) the battery life to 70% capacity will be on the order of 20 year in the Southern California climate. I can still drive to San Francisco, I just won’t do it every week (I don’t now for that matter).

johnchamplinhall, R3937
 
#16
johnchamplinhall said:
I believe that if routine charging is limited to about 80% of maximum mileage (~200 miles) and average daily use to 60 to 70 miles (my present commute) the battery life to 70% capacity will be on the order of 20 year in the Southern California climate. I can still drive to San Francisco, I just won’t do it every week (I don’t now for that matter).
Click to expand...
Thanks for an informative, fact-based post, John. I wanted to emphasize your final conclusion--it's a very powerful one.
 
#19
Great post.

I have a question then about what Tesla recommends and what you have calculated. Tesla recommends nightly charging. For the majority of us, this will be more than enough time to charge the car before we use it the next day. Unless I am mistaken, there presently is no way to set the charging max. Unless I am mistaken, the standard charge goes to 90%. If this is true, how does your model change for us driving 60-70 miles per day? Someone please correct me if I am wrong with these numbers.

(I also distantly remember reading something using 80% of battery capacity -- top 10% and bottom 10%; maybe this is the case.)
 
#20
kevincwelch said:
(I also distantly remember reading something using 80% of battery capacity -- top 10% and bottom 10%; maybe this is the case.)
Click to expand...

That was probably referring to the Roadster. I believe a standard charge on the Model S goes to 90% then down to 0% SOC (it still keeps something at the bottom that you can't access otherwise it wouldn't be able to sit at empty for a month without ruining the battery pack).
 
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