Stoaty
Posts: 4488
Joined: Fri Jun 18, 2010 9:50 pm
Delivery Date: 12 Jun 2011
Leaf Number: 3871
Location: West Los Angeles

Re: Battery Aging Model

Sun Oct 14, 2012 9:24 pm

TickTock wrote:I almost never park in the sun (usually get one of the covered parking spots). For a couple of months I was plugging in at work and taking advantage of the pre-cool feature before I left the office (but very rarely actually charged there - only if I had a far errand over lunch). Since the AC condenser seems to dump the heat into the cavity above the battery, I wouldn't be surprised if that contributed.
Here are the numbers I managed to jot down. Keep in mind *I* didn't see the actual numbers either and read these values off the graph. I would guess I am within 0.5%.
  • Age Nom Boston Phoenix
    0.5 ??? 94% 92%
    1.0 92% 93% 89%
    2.0 88% 90% 85%
    5.0 80% 84% 75%
Thanks. Those numbers are pretty close to what I guessed. I figured out a way to tweak my model by applying an empirical correction factor to almost exactly match the graph you jotted down from Nissan. The observed corrections needed to come up with the right numbers plotted against the number of years are linear, with a correlation coefficient of 0.9995. It needs a bit more work, but I think I can improve the predictive value. After that, I need to plug in more data to see if it matches up.
2011 Leaf with 62,000 miles given to Nephew
2013 Tesla Model S85 with 251 miles rated range at full charge
Leaf Spy Manual
Battery Aging Model Spreadsheet

Herm
Posts: 3765
Joined: Sun May 23, 2010 3:08 pm
Delivery Date: 29 Aug 2012
Location: Timbuktu, Mali

Re: Battery Aging Model

Mon Oct 15, 2012 3:40 am

TonyWilliams wrote:Of course, I think all the data needs to be corrected for 12,000 or 12,500 miles. Just because Nissan pulled some number out of their posterior, it doesn't reflect the average driver.
7500 miles is the average number for Leaf drivers in Phoenix, probably a bunch of wealthy retired geezers.

Stoaty
Posts: 4488
Joined: Fri Jun 18, 2010 9:50 pm
Delivery Date: 12 Jun 2011
Leaf Number: 3871
Location: West Los Angeles

Re: Battery Aging Model

Mon Oct 15, 2012 6:42 am

OK, after tweaking my model it now mathematically reproduces the curves shown in TickTock's graph with very small errors. I am guessing that the additional tweak could represent calendar life loss between the time of manufacture and and the time of delivery to the customer, but I haven't had a chance to change the model to see if that is the correct explanation. That would certainly explain the fact that, for example, at one year the model was off by approximately the same fixed amount for each city. That implies something that was happening to the cars while they were in the same environment. After tweaking, the model now predicts TickTock's loss to within 1% (predicted - 85.7% capacity retained, actual - 84.7%). There is one more piece of data that I need from TickTock (and from other Casa Grande cars if I can get it). How much did you charge to 100%, and how long did your Leaf sit at 100% typically until you drove it?

Here is a graph showing the results of my model:
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2011 Leaf with 62,000 miles given to Nephew
2013 Tesla Model S85 with 251 miles rated range at full charge
Leaf Spy Manual
Battery Aging Model Spreadsheet

DaveinOlyWA
Posts: 14221
Joined: Sat Apr 24, 2010 7:43 pm
Delivery Date: 16 Nov 2019
Leaf Number: 319862
Location: Olympia, WA
Contact: Website

Re: Battery Aging Model

Mon Oct 15, 2012 7:06 am

hill wrote:After seeing what's expected best case scenerio, worst case scenerio . . . . I must admit I am one of the VERY lucky ones - still getting 100 miles per . . . and 280 gids (knock on wood)
Gary beginning to think we are simply seeing a much higher than expected variance between pack characteristics straight from the factory. i propose, your balance was a tighter match than average. in the new pack stage; micro differences may extrapolate to extreme differences in longevity

a bit OT; but do you have covered parking at work?
2011 SL; 44,598 mi, 87% SOH. 2013 S; 44,840 mi, 91% SOH. 2016 S30; 29,413 mi, 99% SOH. 2018 S; 25,185 mi, SOH 92.23%. 2019 S Plus; 412 mi, 99.72% SOH
My Blog; http://daveinolywa.blogspot.com" onclick="window.open(this.href);return false;

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TonyWilliams
Posts: 10091
Joined: Sat Feb 19, 2011 1:48 am
Location: San Diego
Contact: Website

Re: Battery Aging Model

Mon Oct 15, 2012 7:15 am

Herm wrote:
TonyWilliams wrote:Of course, I think all the data needs to be corrected for 12,000 or 12,500 miles. Just because Nissan pulled some number out of their posterior, it doesn't reflect the average driver.
7500 miles is the average number for Leaf drivers in Phoenix, probably a bunch of wealthy retired geezers.
And they magically knew that is who would buy the car, and how far they would drive? Is each owner required to hit "OK" every time?

No, they pulled it out of their posterior to cover their posterior. Surely, it was based on 12,500 miles, and then when they saw things weren't going to work well, they "reindexed" 76% and 7500 miles.

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RegGuheert
Posts: 6419
Joined: Mon Mar 19, 2012 4:12 am
Delivery Date: 16 Mar 2012
Leaf Number: 5926
Location: Northern VA

Re: Battery Aging Model

Mon Oct 15, 2012 7:57 am

Stoaty wrote:From what I have read, calendar life loss does follow the square root of time, so presumably the calendar life loss will slow.
From what I can find in posted literature, that type of degradation is what researchers use when they are fitting calendar life to data measured over the first 10 DAYS of the cell's life. In each case where researchers have actually MEASURED calendar life for many months, the degradation is at least linear and in many cases the degradation accelerates with time.

I have previously posted links to a paper that did measurements back in 2003. Here is a more recent study: 2007 Calendar Li-ion Pouch Cell Calendar Life Study - Zhang and White. Granted, this is still on a different chemistry, but it shows the same effect. Interestingly, the degradation is linear unless the temperature is above 15C: at 25C and above it rolls off a cliff at some point. The researchers suggest there may be different mechanisms active at the higher temperatures.

I will say that the data we have for the LEAF battery so far does not look very promising, either. Some LEAFs with low miles have been well-pampered and still appear to be degrading quickly.

So I will ask, does anyone have *measured* data for pouch Li-ion cells showing calendar degradation that is linear for many months or years?
RegGuheert
2011 Leaf SL Demo vehicle
10K mi. on 041413; 20K mi. (55.7Ah) on 080714; 30K mi. (52.0Ah) on 123015; 40K mi. (49.8Ah) on 020817; 50K mi. (47.2Ah) on 120717; 60K mi. (43.66Ah) on 091918.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

DaveinOlyWA
Posts: 14221
Joined: Sat Apr 24, 2010 7:43 pm
Delivery Date: 16 Nov 2019
Leaf Number: 319862
Location: Olympia, WA
Contact: Website

Re: Battery Aging Model

Mon Oct 15, 2012 9:26 am

the difference in chemistry cannot be ignored. even for the chemistry Nissan uses, it can be tweaked to favor cycling, power output or temperature resistance.

another thing about a lot of batteries is that "talk time" is favored so batteries are purposefully charged slightly over recommended levels which in essence, creates an artificial linear degradation curve. granted its cellphones but the idea is still out there
2011 SL; 44,598 mi, 87% SOH. 2013 S; 44,840 mi, 91% SOH. 2016 S30; 29,413 mi, 99% SOH. 2018 S; 25,185 mi, SOH 92.23%. 2019 S Plus; 412 mi, 99.72% SOH
My Blog; http://daveinolywa.blogspot.com" onclick="window.open(this.href);return false;

Stoaty
Posts: 4488
Joined: Fri Jun 18, 2010 9:50 pm
Delivery Date: 12 Jun 2011
Leaf Number: 3871
Location: West Los Angeles

Re: Battery Aging Model

Mon Oct 15, 2012 9:33 am

I realized there is one additional factor in TickTock's case that led my model to slightly under predict his capacity loss: his car has been through most of 2 hot summers during the 1.3 years of ownership. My model is only accurate for a whole number of years, and will have slight inaccuracies for partial years. Aging will be different during different seasons, which is not easy to account for. One would have to calculate an aging factor for each month of the year (not something I plan to do in general, although I might end up doing it for Phoenix and Boston).
2011 Leaf with 62,000 miles given to Nephew
2013 Tesla Model S85 with 251 miles rated range at full charge
Leaf Spy Manual
Battery Aging Model Spreadsheet

Stoaty
Posts: 4488
Joined: Fri Jun 18, 2010 9:50 pm
Delivery Date: 12 Jun 2011
Leaf Number: 3871
Location: West Los Angeles

Re: Battery Aging Model

Mon Oct 15, 2012 7:41 pm

I tried to work backward to see where the empirically derived battery aging factors that make my model work could have come from. It turns out that I can get the factors quite close by assuming that the speed of chemical reactions doubles for every 15.2 degrees C., rather than every 10 degrees C. Again, not saying this is right, but I did find it interesting. More info to come as I discover (or invent?) it. :lol:
2011 Leaf with 62,000 miles given to Nephew
2013 Tesla Model S85 with 251 miles rated range at full charge
Leaf Spy Manual
Battery Aging Model Spreadsheet

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surfingslovak
Vendor
Posts: 3809
Joined: Mon Jun 13, 2011 1:35 pm

Re: Battery Aging Model

Mon Oct 15, 2012 7:54 pm

Stoaty wrote:More info to come as I discover (or invent?) it. :lol:
Fascinating, please keep up the good work. Wish I had time to participate more actively in this thread. Image

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