Capacity Loss on 2011-2012 LEAFs

[TLeaf]

TickTock's meeting with Nissan certaintly sounds interesting. Will be curious to hear your indepth analysis of it when life slows down for you a bit. I find it interesting that you would say if you drive 50+ miles a day in Phoenix that you would need a new battery in 5 years.. So those guys that drive less, or leave their cars parked are far better off? Only reason I ask is cause I drive my car predominantly 20 miles a day, but in the summer it has gotten up to 105F here in Norfolk, and ever since this problem started creeping up I have been watching like a hawk. While I hope they step up to the plate and replace the Phoenix batteries it would be great to know if mine is better off. Replacing the battery every 5 years would be insane though. If most only have 76% left now what would be left at the 5 year mark? If ScottY's car was any indication once it starts degrading it keeps going.

I think the implication is that a person could expect to have a single-charge range of around 50 miles within 5 years, so if your commute is only 20mpd, and you don't mind charging every night, then I think you're going to fine for many years to come.

[RegGuheert]

If ScottY's car was any indication once it starts degrading it keeps going.

+1

I've always been skeptical of the claim of reduced degradation ove time for EV's, even though you see it in practically every battery cycling curve published. As I have pointed out previously, some calendar life curves actually show degradation accelerating with time. Since cycling tests often are accelerated to get results more quickly, the effects of calendar life degradation are not fully understood. I suspect this may be the case with Nissan, since they focus a lot of their discussion on "miles per year".

But, thinking about this further I will state that normal battery cycling done for testing does NOT match what EV drivers do with the car.

In a battery test, the battery charges until it gets to some predetermined condition and then discharges until it gets to some other predetermined condition. This approach has the nice feature of indicating a capacity between those two points with each cycle.

In real life, you don't keep driving until your car gets to turtle (unless you are Tony Williams creating a range chart!), you stop driving when you arrive at your destination. If you are a commuter, then you stop when you get to work and the daily discharge would be about the same number of kWh, split into two partial discharges.

So, if you wanted to construct a life-test for a LEAF battery that would more closely predict what customers see, you should charge to the 80% or 100% cutoff each cycle and then discharge a predetermined number of kWh each cycle. Then charge to 100% and discharge to 0% once each seven cycles to find the "weekly" capacity. This will result in the %DOD increasing as the battery degrades, allowing for better predictions about how the rate of degradation changes as the battery deteriorates. The battery should be considered failed when it is no longer possible to discharge the number of kWh set for the test. By doing a range of such tests, you will find that the life of the battery is *dramatically* shorter for a customer planning to commute 70 miles than one planning to commute 20 miles, since not only does the battery degrade faster, but the failure criterion is also much more difficult to meet.

Of course, this still does not account for full the impact of calendar degradation which is more significant for customer applications since more time passes in the same number of cycles.

Also, most so-called "battery" tests are done on a single cell, not the entire battery. As a result, the impact of cell imbalance and the BMS do not come into the picture. In the case of the LEAF battery, I think a such a test with the full battery might shed some light on balancing issues that we all experience when we only charge to 80%.

[DaveinOlyWA]

what about other LI chemistries? granted not the same but lets look at them. cellphone batteries tend to lose a bit real fast and then slow down for a bit then they get to a point then seem to go downhill fast.

now, i have a phone and to be honest with ya, never paid that much attention to how soon i started losing battery capacity until i got a phone that simply did not have the right size battery to begin with.

my Droid Bionic's original battery from day one was turning orange by lunch time from a full charge every night. i made the decision less than two weeks later to get an extended battery which was great and lasted all day with battery indicator in the green. that lasted a month (sept 2011) . then it was orange or near orange at night before going to bed. fast forward a year later. now, its orange or red (sept 2012 (a few times had to switch batteries since i still have the little one which is still near new since it was used less than two weeks)

now the decline between sept 2011 to sept 2012 was pretty gradual. obviously a very unscientific observation we have here but if my degradation would have been the same from the first month to now, i would have no battery left at all.

now, something i wish i would have done right away is i am only charging to 90 % which i started in Aug to see if i can eek this battery out longer. i am pretty much charging at least a little bit 2-4 times a day including charging in car which is something i did not do until recently.

now back to my earlier statement. different chemistry, anecdotal observations, no real way of measuring power usage, etc... but just saying

[Pipcecil]

hmmm that take away from TickTock is very disconcerning for me. While Texas is not as harsh as Phoenix or other parts of Arizona, we do have it pretty hot here. I do exceed the 50 miles per day and go, on average 55 - this assumes to work and back only, not any additional side trips to the store or anything. I average about 1700 per month, which is around 55 miles per day (including weekends). To know that my car will be at end life in ~5 years is very troubling. I am assuming that Nissan is still sticking with end-life being 70% capacity remaining in the battery.

The scary part on that is I took out a 6 year loan for my car (yes, I know shame on me, but I am quite young and this is my first real car purchase I didn't have the luxury of a higher income from years of experience in the workforce , I scrapped to afford the car but, at the time, was worth it because of the new tech of an EV!). So the idea that my car will be at the end of life and I could STILL owe on it...thats bad. I usually expect any car to last about 10 years if you do all the regular maintence, etc. You shouldn't have to baby any car to get to 10 years, but you can't ignore things like spark plug failures and check engine lights. Anything beyond 10 is icing on the car with usually my goal to hit 200k.


The usuable reliable life of a car under 5 years is really going to be devistating. Not only will that affect loan for the car (i.e. what lender now would give a 6 year note in phoenix if they new that info!) That also affects resale and insurance values too!

[DaveEV]

hmmm that take away from TickTock is very disconcerning for me. While Texas is not as harsh as Phoenix or other parts of Arizona, we do have it pretty hot here. I do exceed the 50 miles per day and go, on average 55 - this assumes to work and back only, not any additional side trips to the store or anything. I average about 1700 per month, which is around 55 miles per day (including weekends). To know that my car will be at end life in ~5 years is very troubling. I am assuming that Nissan is still sticking with end-life being 70% capacity remaining in the battery.

The scary part on that is I took out a 6 year loan for my car (yes, I know shame on me, but I am quite young and this is my first real car purchase I didn't have the luxury of a higher income from years of experience in the workforce , I scrapped to afford the car but, at the time, was worth it because of the new tech of an EV!). So the idea that my car will be at the end of life and I could STILL owe on it...thats bad. I usually expect any car to last about 10 years if you do all the regular maintence, etc. You shouldn't have to baby any car to get to 10 years, but you can't ignore things like spark plug failures and check engine lights. Anything beyond 10 is icing on the car with usually my goal to hit 200k.

Some numbers:

1700 mi/month = 20k mi / year = 100k mi after 5 years and 200k mi after 10 years.

I think we all agree that the EPA range of 73 miles is possible to hit when the car is new while maintaining a small bit of buffer (typically get there around LBW or a bit after that if you drive a sedate 60-65 mph at most with a bit of surface street driving mixed in). So let's call the "new" range to turtle 84 miles and subtract 16 miles to LBW since people in general don't like to go much below LBW if they can help it for "new" range of 68 miles without too much anxiety.

Nissan's original claims is that you'll have 80% after 5 years and 70% after 10 years.

80% of 68 miles = 54 miles
70% of 68 miles = 48 miles

But that assumes that LBW scales down as total capacity decreases, which it doesn't. At 80% capacity remaining you'll get LBW around 51 miles and at 70% you'll get LBW around 43 miles (total range 67 mi / 59 mi respectively).

And don't forget that this is range in ideal conditions and using whatever crazy annual miles Nissan has used for their estimates. We have assumed 12k mi/year (reasonable assumption since the 8-year/100k mi warranty against defects works around to 12.5k mi/year) - but some of Nissan's statements indicate that they are assuming many, many less. In which case we might as well throw the 80%/70% numbers out the window.

Certainly if you are driving 20k mi/year, you should not be expecting 80% capacity remaining after 5 years unless perhaps you life in Seattle or some other cool place. You probably should be expecting 70%. If replacing the pack some around the 5 year mark is going to present you a financial hardship - frankly you are up sh*t creek without a paddle at this point. You can only hope that the battery is cheap to replace. Personally, I'm hoping that the $5k replacement price that is rumored to exist is accurate - that would make the replacement price $0.05/mi over 100k mi which is reasonable. But I'm afraid this is likely to be optimistic by $3-5k unless Nissan is able to eat some of the cost (maybe they will be able to recover a good amount of the cost by using the old batteries in a stationary application?).

If you expect to keep the car for 10 years driving 12k mi/year - don't expect to comfortably exceed much more than 45 miles/charge unless you are able to top-off during the day. And certainly if you drive a lot, it's quite clear that you should not be buying this car until Nissan provides actual cost to replace the pack and real data on how the pack will last.

Nissan needs to disclose this type of information up front in a reasonable manner that people can use to reliably estimate battery pack life for their usage patterns. It's very clear that they have their own internal data which they aren't sharing, and apparently real-life usage is matching up fairly well with that data.

Managing customer expectations of actual range and capacity loss over time is absolutely critical to keeping customers happy. People will also assume that any generally stated degradation figures are worst case - it's human nature to be an optimist.

Nissan's complete failure in this regard has resulted in really the worst case scenario - an angry mob of LEAF owners wielding pitchforks demanding that things be made right when if they had provided the information up front - those angry owners never would have bought the LEAF in the first place - or at least they would have expected the capacity and range loss they are seeing now.

[palmermd]

nice summary drees.

[TickTock]

Here's my receation of the graph I think is most pertinent to all owners/buyers to decide individual course of action. The actual dots are numbers I wrote down, I filled in the gaps from memory based on the shape. Indeed there is a precipitous drop in capacity in the first 6 months and then the degradation slows and continues to slow over time. The key thing to notice is the 80%@5years we've all been using to base our decisions is actually only the median value and not what a Phoenician can use as an "expected value" These curves are based on average mileage per area: 7500 for Phoenix (I don't recall what the Boston number was except that it was higher then Phoenix). I drive almost 2X that which explains why I am sitting well below the Phoenix predicted curve at 84.7@1.3years. This data is not LA4, but rather a 32.2A discharge rate to better match 55mph discharge rate.
The axis on the right was not on the graph I was presented. I added that based on the 84.7%SOH Nissan measured and the 74 mile range Tony measured shortly after so I can get a realistic idea how much range I will have at year 5. As you can see it will be well below the 65miles per day I require. If you stick within the 7500 miles per year (~30 miles/day), you should get 65 miles after 5 years and still be quite happy since you only need 30.

[gaswalla]

So, if you live in a hot climate, like Phoenix, they have "corrected" the data by saying one would drive less per year?

The problem with the stated ranges is that you are not supposed to be charging to 100%: if you do, battery degradation suddenly becomes "your fault." Also, one does not drive the car to turtle mode. Thus, having a 60 mile range after 5 years in reality equals: 80% of 60 = 48 miles. Typically, one would like to have one bar left as a cushion for the end of the day (heaven forbid that you might need to make a stop to get milk one day) - thus, I'd say there is a "practical" range of 40 miles per charge - and that is if you drive slowly with no A/C... don't even ask what happens if you want to keep up with traffic and go a whopping 70 mph and keep the temp inside 70 degrees - I'd bet you've got yourself a range of 30 miles... this is horrible!

[Boomer23]

nice summary drees.

+1

[Boomer23]

Here's my receation of the graph I think is most pertinent to all owners/buyers to decide individual course of action. The actual dots are numbers I wrote down, I filled in the gaps from memory based on the shape. Indeed there is a precipitous drop in capacity in the first 6 months and then the degradation slows and continues to slow over time. The key thing to notice is the 80%@5years we've all been using to base our decisions is actually only the median value and not what a Phoenician can use as an "expected value" These curves are based on average mileage per area: 7500 for Phoenix (I don't recall what the Boston number was except that it was higher then Phoenix). I drive almost 2X that which explains why I am sitting well below the Phoenix predicted curve at 84.7@1.3years. This data is not LA4, but rather a 32.2A discharge rate to better match 55mph discharge rate.
The axis on the right was not on the graph I was presented. I added that based on the 84.7%SOH Nissan measured and the 74 mile range Tony measured shortly after so I can get a realistic idea how much range I will have at year 5. As you can see it will be well below the 65miles per day I require. If you stick within the 7500 miles per year (~30 miles/day), you should get 65 miles after 5 years and still be quite happy since you only need 30.

I'm getting really interested in seeing Nissan's list of expected annual driving miles per US city. Gotta see if my current LEAF usage matches Nissan Miles (TM) or if I should Just Take the Prius (TM).