Tesla Model S battery degradation data • Hacker News Board

Re: Tesla Model S battery degradation data

#51

Post by xenadu02 » Thu, Aug 31, 2017, 10:48 PM UTC

RachelF wrote: post #11

mschuster91 wrote: post #2

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.

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?

I thought Tesla switched away from the laptop cells some time ago?

Re: Tesla Model S battery degradation data

#52

Post by apapli » Thu, Aug 31, 2017, 10:48 PM UTC

sqeaky wrote: post #40

seszett wrote: post #22

Earlier quoted context omitted.

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.

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.

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.

Re: Tesla Model S battery degradation data

#53

Post by seszett » Thu, Aug 31, 2017, 10:53 PM UTC

sqeaky wrote: post #40

seszett wrote: post #22

Earlier quoted context omitted.

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.

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.

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.

Re: Tesla Model S battery degradation data

#54

Post by JshWright » Thu, Aug 31, 2017, 10:57 PM UTC

dom0 wrote: post #46

JshWright wrote: post #16

Earlier quoted context omitted.

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)

> human-centric temperature scale One point (100 °F ~ 37 °C) doesn't make a scale.

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).

Re: Tesla Model S battery degradation data

#55

Post by sapienthomo » Thu, Aug 31, 2017, 10:57 PM UTC

peterwwillis wrote: post #37

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.

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.

Re: Tesla Model S battery degradation data

#56

Post by microcolonel » Thu, Aug 31, 2017, 10:58 PM UTC

kbenson wrote: post #8

> 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 thous…

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.

Re: Tesla Model S battery degradation data

#57

Post by hwillis » Thu, Aug 31, 2017, 10:59 PM UTC

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 ~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.

Re: Tesla Model S battery degradation data

#58

Post by maratd » Thu, Aug 31, 2017, 10:59 PM UTC

peterwwillis wrote: post #37

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.

> No secret battery magic going on.

They have a complex cooling system. Your laptop battery definitely doesn't have that. If it did, it wouldn't need to be replaced every few years.

Re: Tesla Model S battery degradation data

#59

Post by user5994461 » Thu, Aug 31, 2017, 11:01 PM UTC

kbenson wrote: post #8

> 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 thous…

It's not just about the thousands separator, the same character is used to separate the decimal part.

It's better to use no punctuation at all if you want to internationalize.

Re: Tesla Model S battery degradation data

#60

Post by fish_fan » Thu, Aug 31, 2017, 11:01 PM UTC

peterwwillis wrote: post #37

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.

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.