Battery Ageing Model

JejuSoul said:

The AVT data is from the Intertek site in downtown Phoenix. Summer in Phoenix is very hot and sunny. You can look at in Google Earth. The cars sit on the tarmac and charge during the day without any shade. This is the worst possible way to treat a Lithium Ion Battery without dropping it into a volcano. I used to think that having the EV testing center in Phoenix Arizona was a bad idea because it gives the worst possible results. Looking at the above data however I realise that it is good to have worst case scenario data. It is the reason my priority topic for the next few months will be how to keep the battery cool during a hot summer.

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Is there also anything known about the charging behavior? Because what I read is that it is better to charge to 80%, do not keep charge % to 100% long, do no deep discharge often, keep the average charging % to 50% is the best, charge to desired level just before leaving. And now and then (once a month?) do a battery calibration (from 100% to below 20% and back to 100%). This should really help the lifetime of the battery.

My daily work commute is 2 times 40 km, so I usually charge at work till 80% (solar panels are installed at work). 40 km commute takes about 20% away (dependent of summer/winter and speed of driving), and recharge the next day at about 40% back to 80%. Only when the range is needed, I charge just before leaving to 100%.

This is also interesting information about battery aging:
http://mat4bat.eu/wp-content/uploads/2014/03/Calendar-ageing-modeling-of-Lithium-Ion-batteries_Gyan_Renault.pdf

JejuSoul said:

The AVT website has updated their deterioration data. - https://avt.inl.gov/vehicle-button/2015-kia-soul
I have added the latest data into an Excel spreadsheet. The Kia Soul EV is behaving completely normally compared to all the other EVs being tested in Arizona. Much better than the Leaf and iMiev. Exactly the same as the Ford Fusion. Similar to the BMW i3, Mercedes B class, eGolf and Spark.

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Thanks for the info, I have been checking regularly for a long time to see the updated data. This is very interesting indeed. In Norway, we have a 7 year/150.000km warranty on the batteries. The warranty states that the battery will have atleast 70% remaining (a degradation of 30%) after 7 years/150.000km. As far as I can tell, Kia is likely to have to change the battery pack on some vehicles at least. Off course, we don't have the same temperatures as they do in Phoenix, but all that degradation seen in the AVT reports cannot be all due to high temperature.

I try to keep my battery as much as possible at 44%-64% SOC (3.7V to 3.9V pr cell) to avoid as much stress on the battery as possible. I also avoid parking on tarmac which has been heated up by the sun in the summertime.

ZuinigeRijder said:

This is also interesting information about battery ageing:
http://mat4bat.eu/wp-content/uploads/2014/03/Calendar-ageing-modeling-of-Lithium-Ion-batteries_Gyan_Renault.pdf

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Thanks. That document is the best discussion and analysis of battery ageing I have seen. The two important topics -
1/ Never let the battery get to 60C. Anything above 40C is bad.
2/ Avoid leaving the car at 100% SOC for any length of time.
There is nothing about avoiding Chademo or L3 charging.

I too normally charge my car between 30% and 80%. I sometimes go to 100% when needed, but do that just before I leave. I will probably avoid doing a calibration check or range check in the summer months. But summer is when we use the car most going to the beach. Strategies to keep the car cool are important for me.

Birkeland said:

Of course, we don't have the same temperatures as they do in Phoenix, but all that degradation seen in the AVT reports cannot be all due to high temperature.

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Obviously cars in cooler climates do degrade but nowhere near as badly as in Phoenix. Note even cars in Phoenix do not degrade as badly as the AVT cars if treated well. (see the Phoenix thread in this forum). The data we have to prove this is from the early N issan L eaf and iMiev. For example here is a graph of the battery history of IMiev owners collected by http://www.evpositive.com/evbatmon-for-i-miev.html (distances are in km)

JejuSoul said:

ZuinigeRijder said:

This is also interesting information about battery ageing:
http://mat4bat.eu/wp-content/uploads/2014/03/Calendar-ageing-modeling-of-Lithium-Ion-batteries_Gyan_Renault.pdf

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Thanks. That document is the best discussion and analysis of battery ageing I have seen. The two important topics -
1/ Never let the battery get to 60C. Anything above 40C is bad.
2/ Avoid leaving the car at 100% SOC for any length of time.
There is nothing about avoiding Chademo or L3 charging.

I too normally charge my car between 30% and 80%. I sometimes go to 100% when needed, but do that just before I leave. I will probably avoid doing a calibration check or range check in the summer months. But summer is when we use the car most going to the beach. Strategies to keep the car cool are important for me.

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On the same site, in an overview presentation there is something stated about Chademo/L3 charging:
http://mat4bat.eu/wp-content/uploads/2015/07/MAT4BAT_Project_S-Martinet.pdf

quoting:

In cycling mode, the degradation is mainly accelerated with the increase of the charge C-rate, the increase of the SOC of end-of-charge, and the decrease of the temperature. Autopsies reveal that the dominant ageing factor in this triptych of worst conditions is the lithium plating mechanism. Finally, these results tend to indicate that fast charges (here up to 3C corresponding to a charge in ~20 minutes) are not prohibitive for battery lifetime, provided that the temperature and/or the SOC of end-of-charge are well managed.


Here are some more interesting publications from mat4bat.eu:
http://mat4bat.eu/wp-content/upload...understanding-from-autopsies_Delaille_CEA.pdf
http://mat4bat.eu/wp-content/upload...g-of-Lithium-Ion-batteries_Grolleau_EIGSI.pdf (page 24-31 shows interesting information charging with 1C, 2C and 3C at 5, 25 and 45 degrees Celcius. Page 35-43 also show interesting figures).

JejuSoul said:

Elmil said:

... this probably also explains why some cars show larger difference, between cumulative energy in and out, than others.

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Can you explain why you say this. It doesn't match the data I have collected for our cars. What I see is that initially the cumulative discharge is higher because the battery is manufactured fully charged, but after that the cumulative charge is higher by about 2%. This is consistent with all the cars we have measured so far.

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Yes, you are right, my speculation was that I thought there were one or two cars with greater difference in those numbers. Can't find that data now though..

However, I still see no explanation to why the energy/charge counters are changed much more than what would be possible at the actual available power.

On my own car's deterioration values, last week was a setback, when they got worse 3 times that week. They are now 10.8%/9.4%, up from 7.9%/6.5%. I think maybe this has to do with the highway-ish driving to the dealer, which is 2x100km and mostly CC at around 100km/h. My everyday work commute is more varying and 40-80km/h, so the deviant driving pattern might have triggered the change. Maybe..

@ZuinigeRijder: Thanks for the Mat4Bat links. Good resources!

JejuSoul said:

The AVT website has updated their deterioration data. - https://avt.inl.gov/vehicle-button/2015-kia-soul
I have added the latest data into an Excel spreadsheet. The Kia Soul EV is behaving completely normally compared to all the other EVs being tested in Arizona. Much better than the Leaf and iMiev. Exactly the same as the Ford Fusion. Similar to the BMW i3, Mercedes B class, eGolf and Spark.

Click image for bigger graphic.

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You might consider that that graph is misleading, in that it uses distance (and not also time) as the single indicator of battery ageing, and more significantly, it disregards the variable exposure of the different BEVs to extreme Phoenix Summer temperatures.

It appears to compare results for the Soul and Focus after only one summer of testing, with results for an I-MIEV over two (or three) summers, and with four LEAFs, two which have suffered two summers of exposure to Phoenix temperatures.

For example, the linear LEAF results, in the graph would look much closer to the linear results shown for the Soul if its endpoint were placed at 84.7% capacity remaining (the average for the two LEAFs with one Summer of testing) rather than at ~82.5%,where you placed it.

As I summarized last week at the Soul thread at MNL:

...The two 2103 LEAFs which baseline at ~500 miles, with one summer of use averaging ~15.5 k miles over just under 15 months, show ~15.3% average capacity loss, or ~3.7 kWh average.

The three 2015 Souls which baseline at ~400 miles, also with a different summer of use averaging just under 12k k miles over just under 11 months, show ~10.5% average capacity loss, or ~3.2 kWh average...

...showing slightly over 1% capacity loss per month for the LEAFs, as compared with slightly under 1% capacity loss per month for the Soul...

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http://www.mynissanleaf.com/viewtopic.php?f=10&t=13531&hilit=soul&start=1000

edatoakrun said:

...The two 2103 LEAFs which baseline at ~500 miles, with one summer of use averaging ~15.5 k miles over just under 15 months, show ~15.3% average capacity loss, or ~3.7 kWh average.

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The testing data for the 4 Nissan Leafs has been updated. Look at Vehicle #0646 and Vehicle #9270. All 4 of the 2013 LEAFs began testing in early 2014. All 4 have results upto spring 2015. All 4 have have 1 summer of results included. My graph shows the average for all 4 cars.

Your comments miss the main point of analysing the Phoenix data. All Lithium Ion batteries degrade badly in extreme heat. This is worst case scenario data. The point is to create strategies to avoid extreme heat.

JejuSoul said:

The AVT data is from the Intertek site in downtown Phoenix. Summer in Phoenix is very hot and sunny. You can look at in Google Earth. The cars sit on the tarmac and charge during the day without any shade. This is the worst possible way to treat a Lithium Ion Battery without dropping it into a volcano. I used to think that having the EV testing center in Phoenix Arizona was a bad idea because it gives the worst possible results. Looking at the above data however I realise that it is good to have worst case scenario data. It is the reason my priority topic for the next few months will be how to keep the battery cool during a hot summer.

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="JejuSoul"
...Why would you cherry pick the two best cars ???

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I didn't pick the two best cars, I picked those two which only had ONE Phoenix Summer of use, to most accurately compare them to the three Soul EVs test regime.

="JejuSoul"...All 4 of the 2013 LEAFs began testing in early 2014. All 4 have results upto spring 2015. All 4 have have 1 summer of results included..

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That is incorrect.

This LEAF has been tested over 20+ months, including two full summers, 2014 and 2015:

https://avt.inl.gov/sites/default/files/pdf/fsev/batteryLeaf0646.pdf

And this LEAF's baseline starts at 6,258 miles, and already had completed 546 miles as of 5/14/13 (see maintenance records) indicating it was tested over 22+ months and over two full summers, 2013 and 2014.

https://avt.inl.gov/sites/default/files/pdf/fsev/batteryLeaf5045.pdf

="JejuSoul"...Your comments miss the main point of analysing the Phoenix data. All Lithium Ion batteries degrade badly in extreme heat...

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Correct.

Which is why you should compare BEVs with similar exposure to the hottest seasons, as well as similar miles driven and vehicle age, if you want to make valid comparisons of battery degradation.

In fact there are many differences in the procedures used by the AVTA in its tests of the varying BEVs, which is why I prefaced my comments on the Soul thread at MNL with a caveat, and only a general prediction:

...Not enough data yet (IMO) to make a valid comparison to the (2013 is the most recent MY) LEAF capacity loss results.

On the positive side, The 2015 Soul E's seem to be using only ~5% more Wh/mile than the 2013 LEAFs, so their rudimentary ATM systems don't seem to impose the large efficiency penalty as does the Ford Focus E's (which seems to require ~20% greater Wh/m than the LEAFs) the only other BEV with a ~year or more of AVTA battery results posted.

IMO, it is likely that a few years from now the AVTA data from Phoenix will show that if you live in any climate this hot (and especially if you utilize high kWh throughput in the Summer) you will either have to pay a hell of a lot to cool your pack, or you will have to accept considerably faster degradation than that experienced by BEVs in cooler climates.

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http://www.mynissanleaf.com/viewtopic.php?f=10&t=13531&hilit=soul&start=1000

edatoakrun said:

I didn't pick the two best cars, I picked those two which only had ONE Phoenix Summer of use, to most accurately compare them to the three Soul EVs test regime.

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So the 4 Soul EVs are to be counted because they have driven 1 winter, 1 spring, 1 summer and 1 fall.
But the Nissan Leaf must only be counted if it has 2 winters, 2 springs, 1 summer and 2 falls.

Is there something particular about the second summer of driving that makes it so much worse than the first? Why would the average for the year not be the same?

="JejuSoul"

edatoakrun said:

I didn't pick the two best cars, I picked those two which only had ONE Phoenix Summer of use, to most accurately compare them to the three Soul EVs test regime.

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So the 4 Soul EVs are to be counted because they have driven 1 winter, 1 spring, 1 summer and 1 fall...

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Only three of the Souls have reports covering summer degradation, all during the year 2015.

="JejuSoul" But the Nissan Leaf must only be counted if it has 2 winters, 2 springs, 1 summer and 2 falls.

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The two LEAFs with one summer of degradation (2014) reports cover the periods of ~2/14 to ~4/15, both between 14 to 15 months, not "2 winters, 2 springs, 1 summer and 2 falls".

This probably means a cooler average ambient temperature exposure for the LEAFs compared to the Souls, depending on the variations in Phoenix temperatures between the different years.

However, every one of BEV test fleets has different calendar exposure. The Focus Es, for example have many more months and a much hotter mix of months, of testing than do the three Souls

So plotting the Focus Es on the same graph as the Soul Es by miles driven, significantly overestimates the Focus fleet's actual comparative degradation.

This is why I think it is inherently misleading to post comparative degradation results using a chart with miles driven as an axis, without controlling for other known degradation factors, such as time and temperature.

="JejuSoul"
...Is there something particular about the second summer of driving that makes it so much worse than the first? Why would the average for the year not be the same?

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Actually, looking at the totality of AVTA testing for the LEAFs going back many years, it appears their pack capacity degradation may tend to slow down after the first year.

But that has nothing to do with the fact that if you look at degradation in a climate as extreme as Phoenix for time periods of over one year and less than two years, any period including two Summers will probably always show far more average monthly degradation than any period including only one Summer.

As for the second-year-degradation of Soul packs, that's something we will only know, after we see the second year of data.

When I commented on MNL about the AVTA Volts holding up very well over very long periods and high mileages (>100,000 miles) you replied that the cars were rarely plugged in and driven on EV and this is the reason for the lack of pack degradation. Age and ambient temps were not a factor in your rebuttal.

Does time degradation not affect Volts? It seems that when Leafs are degrading quickly it's because of time and ambient temperature averages, not miles. When Souls are degrading slower than Leafs it's because the packs haven't had as much time under their belts and total mileage is dismissed. When Volts don't degrade it's because...they haven't had enough EV miles even though the packs are as old or older than the Leafs' and exposed to the same high Phoenix temps.

Just reading your posts it often seems as though you're making a concerted effort to twist data to show that TMS systems are entirely useless at slowing degradation and there's absolutely no way that Leafs degrade any faster than competing vehicles with thermal management. Perhaps I'm merely misunderstanding your intentions but it sure comes across that way to me through text. Naturally it can be difficult to understand someone's point through Internet forums.

I find it hard to believe that hundreds of engineers at these automakers have developed systems to slow degradation and all of their efforts are for naught, that they're missing something extremely elementary. GM warrants Volt packs against degradation with a stronger warranty than Nissan, as does Kia, yet I've never heard of a Volt pack being replaced for degradation (of course the Kias are still too young). There are many hundreds of Leaf packs that have been replaced for degradation under the class-action lawsuit warranty in some relatively mild climates (San Diego comes to mind).

Why is it that Chevrolet and Kia can guarantee their packs at no greater than 30% degradation for ten years or 100,000 miles yet Nissan had to be sued into guaranteeing no more than 33.5% over five years or 60,000 miles, and even then so very many Leafs have had their packs swapped?

As a consumer I would (and did) prefer thermal management backed up by a guarantee in writing. I don't see any evidence so far that these systems fail to slow degradation as compared to their passively managed competitors.

That said, I find the data points interesting and am looking forward to seeing how these AVTA charts progress over time and mileage regardless of whether or not the information supports the validation of TMS effectiveness.

You clearly have a lot off off-topic issues to deal with, "mtndrew1".

On-topic:

mtndrew1 said:

...Why is it that Chevrolet and Kia can guarantee their packs at no greater than 30% degradation for ten years or 100,000 miles...

As a consumer I would (and did) prefer thermal management backed up by a guarantee in writing...

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Are either the Spark or Soul BEVs even offered for sale at Arizona dealerships?

If not, maybe that's integral to Kia's and GM's plans for their BEVs to deal with high ambient temperatures...

From the preliminary AVTA data available today, it seems likely to me that most or all Soul EVs driven in a climate as hot or hotter than Phoenix would qualify for replacement long before 10 years or 100k miles are covered.

Depending of course, on how accurately Kia measures battery degradation for warrantee purposes.

I'd be surprised if the Spark did much better, as the increased degradation due to its tiny battery pack (requiring almost twice the cycles to cover the same miles) will probably more than offset GM's more intensive pack cooling system.

On topic, why is it that you dismiss age and ambient temperature on Volt packs older than highly-degraded Leaf packs of similar age in the in the same environment? If these factors are so dominant, as you repeatedly claim across two forums, why doesn't it apply to these cars?

It all just reads as Nissan brand loyalty, apology, and devotion as opposed to objective review of what's happening with these cars in the field.

If Nissan's EVs in San Diego or Sacramento can't make it 50,000 miles without losing a third of their battery capacity requiring a $6,000 warranty repair, that sure seems like a design fail on Nissan's part. The most apparent design flaw seems to be a lack of TMS.

The worst case scenario data we have been looking at recently can be a bit depressing.
How about this to cheer us up.
17,000 Renault Zoe's all above 100% SOH after 3 years.



Found this image at http://insideevs.com/renault-zoe-r240-battery-capacity-23-3-kwh-usable-25-92-kwh-total/

it is copied from this really interesting video presentation.

https://youtu.be/N6sRWGjFx5w

JejuSoul said:

The worst case scenario data we have been looking at recently can be a bit depressing.
How about this to cheer us up.
17,000 Renault Zoe's all above 100% SOH after 3 years.

Found this image at http://insideevs.com/renault-zoe-r240-battery-capacity-23-3-kwh-usable-25-92-kwh-total/

it is copied from this really interesting video presentation.

https://youtu.be/N6sRWGjFx5w

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That IS great news.

BTW... with the lower kw/km energy being consumed due to the warmer weather lately, my GOM is now gradually starting to show greater range available for any given % state of charge. Now, my dash is showing around 15.3 kw/100km... I'd expect well over 155 km on the GOM but that's all I'm getting so far... last week.. same energy stat (15.3), but only 140-145 km on the GOM. This seems to confirm my theory that the GOM uses some time of long-running weighted average, well beyond the energy stats for the last few charges.

That's what I suspected and why I commented on another thread that a concern about reduced range stemming only from a single day's GOM reading is ill-conceived.
Another member commented that temperatures rose on a single day (from cooler weather).. the EV was charged and yet the GOM was showing an unexpectedly low figure.
This is EXACTLY my experience.. and now with more time, the GOM stats are improving.

Bottom line - the GOM is just that.. an educated guess. And if you suspect a problem with your battery, instead of spreading fear and doubt with no hard stats, have your darn battery tested by Kia and come back with actual SOH figures (until we figure out how to pull SOH ourselves!)

mtndrew1 said:

Why is it that Chevrolet and Kia can guarantee their packs at no greater than 30% degradation for ten years or 100,000 miles ...

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If you watch the Renault Zoe video you will hear the battery engineer state that if you extrapolate the degradation trend forward then most of the cars will reach ten years life without needing to replace the battery. The Zoe has LG Chem batteries and a TMS much the same as the Soul EV. I think the reason Kia offers the guarantee is that they too have extrapolated a trend. (I wonder if anyone knows how the Zoe does in Spain and Portugal - both have had extremely hot summers recently). There is self collected data from Zoe drivers here - http://canze.fisch.lu/battery-health-status/

https://youtu.be/N6sRWGjFx5w

How interesting that the Zoe uses LG Chem cells instead of the AESC ones in the Leaf and e-NV200, seeing as both automakers are part of the same parent company. I, too, would be interested in Zoe data from hot climates but the general trend looks promising for longevity.

2016Electric said:

Bottom line - the GOM is just that.. an educated guess. And if you suspect a problem with your battery, instead of spreading fear and doubt with no hard stats, have your darn battery tested by Kia and come back with actual SOH figures (until we figure out how to pull SOH ourselves!)

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If we're talking about the same user, I really wish they had watched their ending SOC % at the end of their commute since day 1 to get a feel for actual degradation as opposed to GOM readout.

While my GOM has fluctuated wildly over the last year and a half (trending down dramatically), the SOC percentage consumed during my extremely consistent commute has remained the same over 24,000 miles, implying minimal degradation over that time. I'll have a battery test run at 45,000 miles when I turn the car in just for curiosity's sake. At this rate I'm guessing I'll have less than 15% degradation at that point.

Hey all:

Per Jeju's request and now having the revised OBC entries in torque, here are some additional stats on my vehicle that may be helpful...

Vehicle: 2016 Kia Soul EV (Luxury model with Chademo option), in service as of October 2015

KM total: As of this evening, 8,192 KM

Cumulative kWh CEC: 2,117

Cumulative kWh CED: 2,056

Battery deterioration: Best cell #15, with 0.0% (min det), Worst cell #77, with 3.5% (max det)

Climate: Toronto, Ontario (crappy, need I say more??).. lowest temp was Feb (if I recall correctly, -25C). Highest temp so far +25C last fall and maybe close to that a day or two a few weeks ago. Today was +7C to +10C or so. The vehicle is stored in an underground style parking garage, that usually does not fall below -5C.

Driving style: Mix of highway (100km/hr) and city (50-60 km/hr, in theory!) Trip meter tends to show around 36 km/hr avg. with Toronto traffic when driving just around town with no highway). The vehicle tends to get used during the week as a daily commuter, maybe 20-30 km per day max, at slower city speeds. On weekends, more highway around 80-100 km/hr, trips one way around 30-60 km average. At present, the dash is showing energy use of 15.3 kW/100km. Worst reading was highway use at -25C, lots of wind, and with snow tires mounted. I was pulling around 22 kW/100km that trip easily. Cabin was set to 22C. I might add.. aside from diminished range in the very cold temps, the car performed beautifully - perfectly smooth, quiet, and toasty warm. Average winter energy use was 18-20 kW/100km, mix of city/highway, and cabin set at 22C. I tried to use cabin pre-heat whenever possible (departing from home only, of course).

Charging behaviour: I use delayed charging almost exclusively, to charge the car beginning at 2am, set to 80%. This gives more than enough range during weekday commutes, even in the coldest months. Car probably stops charging usually within 2 hrs (so by 4 am), for the 7am morning commute. On weekends and when I know that I will be driving further, I charge to 100%, but try to plan whenever possible to reach a full charge shortly prior to departure (the timer works well for this).
The vehicle is charged at home, with 2 of three phases (commercial service) for a voltage that hovers between 208 and 2011 volts on average. The charger I built myself (OPENEVSE), which is set at 30 amps. During charging, the OPENEVSE reads 29.3 amp draw on its display when set at 30 (usually), which works out to 210x29.3=6.153kw. The reading I took this evening with the revised OBC codes showed 210.2 volts @ 28.7A and 6.0KW (so pretty close to my calcs).
I should add, in the winter I'd often plug the car in every night to take advantage of morning pre-heating, so SOC usually never fell below 55-60%, or went above 80%. Now that it's warmer, I push it a little more and don't feel compelled to charge every night. Still, I usually don't let the battery fall too low. Lowest ever was maybe 15%-19% or so.

Chademo:
I have used this maybe 3 or 4 times (unfortunately - I wish I had more opportunity to use this), mostly just to try it out. There are almost ZERO fast chargers around here.. and the greater Toronto area is home to around 6 million people. Truly, truly sad state of charing infrastructure at the moment here.. but I digress. Point being, not much fast charging on this battery pack, so far.


Wow.. that was MUCH more than I planned to write.

Thanks for the data. Your car is doing pretty much the same as everyone else. No usable capacity lost.
For example on 11th November 2015 my car was 6 months old.
I had driven 8000km. My deterioration was max 3.5% min 0.1%.
My energy counters were about 20% lower than yours though. Presumably that is the extra cost of heating the car in your cold winter.

If you could post the stats again in a few months or when there is a significant change it helps to average out the figures because any single reading isn't really reliable because of calibration and seasonal factors.

We don't have any climate related effect yet in the data we have been collecting. My car's 6 months of summer heat has degraded the same as yours in 6 months of winter cold. If you read the Phoenix AVTA discussion above it makes it sound that heat will make a massive difference really quickly. Most of the cars we have data for are from cooler climates (Norway, Sweden, Canada). It would be great if someone from a warmer climate could post some data here ( hint ... mtnandrew1 ... hint!)