3.0 Battery Longevity

[Marius]

I am still not sure if the investment is worth it. Sure I have to renew someday but have doubts about the pack that TM delivers. First reports were CAC of 214 and now Bolosky reports 195. This means a degradation of almost 9% in a relatively short time. Until I hear degradation has levelled out I will order.
If I compare the old pack I have lost 10 CAC points in 2 years driving 60.0000 miles. The 3.0 pack is degrading much quicker so it seems.
I am hoping for some after market developments. My simple view is to just purchase 6831 cells of 2 dollar a piece and find someone who is capable to push them all in the pack. Cells are now available of 4000mAh, that is almost double range compared with the original pack.
By the way my current pack is down from 160 to 125 driving 180.000 miles in 5 year.

 

[snd92]

Will be keeping my original pack with 152-154 Ah and 293-298 km on standard charge. I also do not like the additional weight of 3.0

 

[JRP3]

Cells are now available of 4000mAh, that is almost double range compared with the original pack.

I wouldn't count on those cells actually getting their rated capacity or lasting very long.

 

[ion_1]

Data is critical for the decision, in theory, these cells should level off before 15-20% reduction and then be fine for who knows how long (there is no extensive calendar life data). It was really great Tesla offered the replacement pack, but a longer warranty would have be more appropriate and possibly allowed many of us to make the decision to upgrade earlier.

 

[bolosky]

Data is critical for the decision, in theory, these cells should level off before 15-20% reduction and then be fine for who knows how long (there is no extensive calendar life data). It was really great Tesla offered the replacement pack, but a longer warranty would have be more appropriate and possibly allowed many of us to make the decision to upgrade earlier.

I agree completely. Which is why the more 3.0 owners who are willing to share their log files with me, the better. So far, there are only three of us.

I'm especially interested in people who have put a lot of miles on the 3.0.

 

[dpeilow]

I agree completely. Which is why the more 3.0 owners who are willing to share their log files with me, the better. So far, there are only three of us.

I'm especially interested in people who have put a lot of miles on the 3.0.

When I've got some more miles under my belt I will definitely send a file to you. 100 more miles this weekend but the car has stubbornly not moved the CAC.

I know @Kerios will send a file as well when he is back from vacation.

 

[ion_1]

I agree completely. Which is why the more 3.0 owners who are willing to share their log files with me, the better. So far, there are only three of us.

I'm especially interested in people who have put a lot of miles on the 3.0.

Thank you for doing this. It will be a huge help to all those who purchased a 3.0 to track their batt trends relative to others and also for those thinking about an upgrade.

 

[Tovar_Vanek]

Where is Tesla getting the 18650 cells used in the 3.0 packs? Are they already making their own?

 

[JRP3]

From LG Chem.

 

[bolosky]

Here's the latest version of the chart with one new Roadster (#33) added, thanks to slcasner. In addition, I realized that when I was extracting the logs that I was using the reported average brick amp hours, while the CAC that shows up on the VDS is the min Ah. So, I fixed that in this chart. It doesn't really change the shape of the curves very much, but it does move the scale on the y-axis down a little. For reference, my current CAC is about 195, while my reported average is 199.

I notice two other things from this graph. First is the striking difference in slope for #33 from the others. What I can tell from the logs but doesn't show on this graph is that that battery has the longest calendar time from upgrade to when I got the log. That makes me wonder if the degradation we're seeing is based more on time than mileage. I'll make another graph using time on the x-axis to see.

Second, and probably more importantly, is that both #33 and #670 (mine) seem to have leveled off around a CAC of 195 (if anything, mine is curving up a tiny amount). This is consistent with the theory that the cells (or the algorithm that Tesla put in to guess at the cell capacity) have a knee right around 10% degradation. It may well be that they'll retain that capacity for a very long time. If that's so, then I feel much better about the upgrade.

 

[bolosky]

Here's the same data, but using days since upgrade rather than miles since upgrade on the x-axis. Now 425 is a bit of an outlier, and 33 fits right in with the others.

 

[ion_1]

Fantastic set of data! Exactly what we all need to see.
As expected for Li-ion calendar life is more important than number of cycles based on the cycling frequency of the roadster. #33
clearly shows this as a beautiful and extreme example. Thanks so much for including both plots!
These cells in the roadster are cycled for such few numbers and in the nice sweet, stable zone (unless range charged a lot) of potentials,
that cycle life (miles) would have minimal effect.

Considering the number of cells, these batteries all seem to be on similar degradation trajectories. It would
be interesting to see if 425,181, and 670 level off for a month or so like 33 did. Too early to say if any of these batteries
have begun to level off, but these batteries have only approx 10% degradation so far, just below when the leveling should occur
based on hg2 cell data I've seen (if these are really hg2 cells). Nothing concerning so far, but the levelling off of the fade rate is critical.

I've been working on Li-ion cells for a couple of decades and It still amazes me how similar a 7k cell # battery pack can behave. Pre-roadster data I would have never believed anyone that 7k cells would still be functioning in most of roadsters after 5 years, never mind the 9 and approaching 10 years that many have. ESS, Historical game changer.

Re the 3.0 batts, time will tell..in the meantime, many thanks for your efforts and sharing the data analysis. Very cool.

 

[ecarfan]

@bolosky thanks very much for plotting out the data, glad I could contribute the numbers for 425. And happy to see that my degradation curve is inline with others when based on mileage. Surprised my curve based on time shows less degradation. Note: I charge at 56A using the Tesla HPC, and I do a range charge about once a month on average. My Roadster resides in a non-temperature controlled garage and I live in a temperate climate so my resting battery temp probably never drops below 45F.

How about before the end of 2017 we all contribute new data so you can re-plot the curves? This is going to be very interesting...

Here's the same data, but using days since upgrade rather than miles since upgrade on the x-axis. Now 425 is a bit of an outlier, and 33 fits right in with the others.
View attachment 235409

 

[bolosky]

After my post last night Dave Denhart (#181) sent me an updated log that added more than two months' worth of data and which makes it the longest lived 3.0 in the dataset. If it's leveling off, it's a little lower than #33 and #425. I'm still quite curious what this will look like in a year.

 

[bolosky]

And here's the updated days-since-install chart.

 

[ecarfan]

Very interesting.Out of those four 3.0 batteries mine has the lowest miles/time value (it has been driven less over a given amount of time). So my use has been more "gradual".

I hope we can all submit our logs to @bolosky at the end of this year for a new look at the data!

 

[slcasner]

When I saw that first graph (based on miles), I was concerned! The second graph tells the true story because my car does not go that many miles now that I am retired.

I can provide a few details about the shape of my battery's curve. I can't identify a change that corresponds to the beginning of the flat portion of the curve at 90 days. That is November 10, so perhaps cooler weather. In the middle of that flat section was the bed-in procedure for the new rotors, though, which is pretty harsh. The sharp drop at 180 days is a trip to Santa Barbara with range mode charging; the one at 200 is a trip to Napa with range mode charging; and the one at about 253 is another trip to Santa Barbara.

 

[bolosky]

The sharp drop at 180 days is a trip to Santa Barbara with range mode charging; the one at 200 is a trip to Napa with range mode charging; and the one at about 253 is another trip to Santa Barbara.

That's actually really interesting, because the big bump up on mine around 130 days was due to a bunch of consecutive range mode charges, and the smaller bump at 180 days was also a couple of range mode charges. So in your car the range mode charge lowers the CAC, while in mine it raises it. Very strange. It's also consistent with my hypothesis that the car can't really tell the battery capacity without a range mode charge, so most of the curve is just a guess based on usage and time, and when you get to full charge it gets some new info to put into its computation. If that's the case, then I suspect that it's overestimating the effect of miles and underestimating the effect of time.

Or you're just out of balance. Did you let it sit at full range mode charge for some hours to balance?

 

[slcasner]

Or you're just out of balance. Did you let it sit at full range mode charge for some hours to balance?

It would have had 2 hours or so with the full range charge. On days when I do a standard charge it may remain connected for several hours after charging completes.

 

[bolosky]

It would have had 2 hours or so with the full range charge. On days when I do a standard charge it may remain connected for several hours after charging completes.

I don't think that it does much balancing in standard mode on the 3.0 battery, since the standard mode full charge is so low (~80% IIRC). And two hours once or twice per year in range mode probably isn't enough to do it. You might want to try range charging it and leaving it sitting plugged in overnight to see if it helps the CAC. You can tell if it's balancing from the diagnostic screen, of course. It's been my experience with that screen that sometimes it will stop balancing for a short time and then start again, so seeing all 0's doesn't necessarily mean it's really done.

When I got a replacement original battery (which had been removed from the donor car and left sitting for a long while), it took about a week of sitting plugged in at full range charge to balance it, during which time the CAC came way up. I'm sure you're not that bad off, but that's an indication of how slowly balancing can go.