3.0 Battery Longevity

[autoskadestuen]

Hi dpeilow & co.
I am just joining this conversation as I was informed of this thread by a fellow Roadster owner. I also have the R80 upgrade and have noticed a fairly large drop - in 6 months of use from march 2017 to oktober 2017 and only 2.400 km., I had a drop in CAC from 211 til 206. I do not currently know what my initial CAC was, but the car has driven just about 4.400 km since I got the new battery in September 2016.

looking at your diagrams, got me worried. What should we expect? Does this drop in CAC reflect the state of the battery and is it within reason with regards to warranty on the battery?

Anyway, I would like to let you know, that you can add me to the list of people who are concerned and interested in answers at first - and solutions, if relevant. I have not approached Tesla individually as I figure that it makes the most sense for both Tesla and us R80 owners to go through 1 person, to keep the dialogue simple.

Thanks for your effort,

Regards,
Emil Ellefsen
2.5 726

 

[dpeilow]

Thank you for adding you name to the list (and some others that PMed me).

Please send your log files from the car in to @bolosky who is collecting the data and making the graphs.

 

[bolosky]

I got about 8 months' worth of data for #537 from ggr (thanks!), making it the currently oldest battery in the study. It's doing pretty well relative to some of the other older batteries. Probably the most comparable one is #33, which isn't quite as old but is very close in mileage and is about 4 Ah worse. I'm not quite sure what the difference it, although 537 did have a long period of not driving for about two months around day 600, so it may be overdue for a big jump down. Or not, hard to tell.

At the very end, especially on the per day chart, you can see the bump up from a range charge, immediately followed by the drop down from a long drive that pushed the SOC low, which is what I'd predicted when I asked ggr for his logs.

I'm not bothering with the zoomed version of the graph for this update, since the new data is all out of the zoomed range.

 

[mel1800]

Hi,

Having just seen this, I realize it's too late to add my name to the letter, but I'd like to be included as a concerned owner as well.

I have a 2010 2.5 with original battery, and just last month purchased a used 2010 2.0 Sport with original battery and battery upgrade contract (ie, due a 3.0). For now, I'm planning to upgrade to 3.0 battery this September.

Please let me know if I can help in any way.

Thanks.

 

[dpeilow]

Having just seen this, I realize it's too late to add my name to the letter, but I'd like to be included as a concerned owner as well.

I am collating names to send a batch to Tesla as and when I have further communications with them, so please PM me your details if you like.

 

[dpeilow]

Another European owner has come out of the woodwork with CAC down to 193 after ~18 months and 11,000 km. Hopefully that log file will make its way to @bolosky

 

[bolosky]

Adding five months' data to #425, thanks ecarfan. It's one of the higher mileage cars, and it's doing pretty well, all things considered. It's at about the same CAC as 537 was at the same age, but with about 2x the mileage. Still, like the others its losing range at a scary rate, and so far there is no end in sight.

I'm not updating the zoomed version of the per-mile graph, because 425 is a high mileage car, so the zoomed portion hasn't changed with this new data.

 

[Msjulie]

Scary is right...

 

[backmost]

Based on the current slopes, at what time does the capacity of the 3.0 battery reach the same as the original battery?

Scary to spend $29k for an early death wish

 

[JRP3]

Does 209 appear to be leveling out?

 

[gregd]

Based on the current slopes, at what time does the capacity of the 3.0 battery reach the same as the original battery?

Scary to spend $29k for an early death wish

So, here's my back-of-the-carbon fiber trunk lid analysis... Please tell me I've done this horribly wrong.

A new original battery's CAC is reported to be 160ah, and the 3.0 battery appears to be 215ah. So, 55ah more as a base. If you look at the time-focused graph, just eye-balling the 1 year mark it looks like the mid-point of the spread is something like 197ah. Assuming a straight line (it shouldn't be, but it kind of looks like it to me...) you lose 18ah per year, or 55 / (215-197) = 3 years to get down to the original capacity. And if the trend continues to continue, you keep going on down from there. The 80% capacity point for the original battery of 128ah (considered to be end-of-life, though by no means useless) , would be at 4.8 years.

As a comparison, my 8+ year old original battery is at 139.5ah, having dropped about 1ah in the past year.

What we're all hoping for is that the 3.0 battery stabilizes at some point, and the curve stays roughly flat for many years, before dropping off at the end. We're still waiting for that flat spot...

 

[bolosky]

Does 209 appear to be leveling out?

It has about 35 miles on it during its flat spot, and during that time the CAC is exactly the same to seven decimal places. I've seen this pattern before, it looks to me like if you don't drive the car, or only drive it a few miles, the CAC algorithm doesn't run at all. My guess is that it'll just wind up with a downward jump to put it back on the trend line when it's driven again. That's what happened in some of the big steps down on other cars in the chart.

:-(

 

[bolosky]

I'm adding #189. Sparrow sent me the logs a while ago and I managed to completely lose track of them until he reminded me. Sorry about that, and thanks for adding them.

This car is very much of an outlier on the good side. Excepting #2, which only has 109 miles since the upgrade and which hasn't recalculated its CAC since 13 days after the upgrade (and so barely counts), the oldest battery with a better CAC is #277, which is most of a year younger and has slightly fewer miles.

I'm not quite sure what's going on here, it doesn't fit the usual patterns.

That said, even being one of the best cases out there, it's still lost about 5% of capacity in < 2 years and 6K miles, so it's nowhere near as good as the old battery.

I'm including the zoomed version of the by mileage graph, because while this car extends beyond the end of it, it's new and so you haven't seen it before.

And I'm running out of really distinct colors, so I was left with an ugly pale green. Sorry.

 

[dpeilow]

Today @Kerios and I attended a talk in Cambridge by Steve MacManus, VP of Engineering at Tesla.

There were no great revelations for anyone here, but we did manage to talk to him afterwards about the battery issue.

The bottom line is he wasn't aware of it, the letter clearly hadn't reached him (in fact he didn't even know the Director of Western Europe that we sent it to), but he is now and I am going to send an updated/edited version to him with all the details.

 

[dpeilow]

Having just seen this, I realize it's too late to add my name to the letter, but I'd like to be included as a concerned owner as well.

@mel1800 Could you please send me your name and VIN via private message if you wish to add your name to the updated letter? Thanks.

 

[Chris Lockfort]

Interesting that our Leaf brethren have nearly the exact same issue with their upgraded battery packs degrading much faster

Nissan LEAF 30-kWh Battery Degrades More Rapidly Than 24-kWh Pack

 

[gregd]

Interesting that our Leaf brethren have nearly the exact same issue with their upgraded battery packs degrading much faster

Nissan LEAF 30-kWh Battery Degrades More Rapidly Than 24-kWh Pack

I know the Leaf's pack is not thermally managed, but I wonder what chemistry are they using (compared to ours)?

 

[bolosky]

Adding in our 16th 3.0 Roadster, #95 (EU). I got these logs in email, I'm not sure if the owner is a forum member (though I'll be sending him a link to this thread).

It's our fourth highest mileage Roadster, and it looks pretty much middle-of-the-pack for a car that gets driven: slightly worse on the per-days chart and slightly better on the per-miles. It looks like it's been garaged for the winter, and I wouldn't be surprised if the CAC takes a big step down once it comes out again.

I'd update the data for my car, but it's been in the shop for 5 weeks waiting on first the availability of a Roadster technician, then parts that were on the slow boat from Europe, and now more parts. The loaner Model S is nice, but I miss my Roadster.

Amusingly, someone on Reddit started a thread with a picture of my car in the service center parking lot. I'm glad that they enjoyed my plate.

Out with the old and in with the new • r/teslamotors

 

[Msjulie]

They're right, what a size change!

 

[bolosky]

Adding 2.5 months' data to #33. Thanks, slcasner!

It's had about 300 miles driven and lost 1.5 Ah, making it within 0.5 Ah of the lowest CAC in the study. Comparing it to my car (#670), shows how much bigger of an effect calendar life has than mileage. It's about three months older but has about 20K fewer miles on the battery, and has essentially the same CAC.

That said, I wonder how much of that effect is that I occasionally range charge my car, and it doesn't look like #33 has been. My theory is that the CAC estimation algorithm gets more data when it's range charged or driven to very low SOC, and otherwise mostly guesses based on time and mileage. I've consistently noticed that range charging, especially if you do it several days in a row, makes the CAC go up (which isn't to say it's good for the cells, mind you, just the algorithm). If you see the periodic bumps up in my CAC like the large one at ~6500 miles were caused by that. Low SOC seems to make it go down. So it could well be that all of the gain that I've gotten from range charging would happen to #33 if it had a bunch of range charges.

That said, I'm not recommending that you do it, since it is some real load on the battery to do so. But if you do, I'd really love to see the results. My prediction:If you did it enough, you'd get 5-10Ah back. If you got 20Ah back (putting you at ~205, where I was after range charging at similar mileage) then it would mean that the real degradation was due mostly to use and not calendar life.

Without further ado, here are the graphs: