Post Your Battery Degradation Results

[nosuchthing]

I lost my first capacity bar today @ 15,600 miles on my 2011 SLE.
I would contend that my car has been the most "babied" Leaf out there, to wit:

I've Never QC'd; I've never seen more than 6 battery temp bars; My car has never been located where the temperature exceeded 90 degrees (I live 6 miles from the beach in San Diego); I've never driven it to turtle, or even VLBW; I've charged to 100% less than a dozen times since new. About 90% of the time, my battery SOC is between 4-7 bars when not driven for several days.

I have done all of the above and lost the bar at almost 40,000. We had had extensive discussions here at MNL about 100% charging (I still do it daily to this day) and driving and charging and generally treating the car for what it is. A car.

As it turns out all this battery "babying" is/was really all for naught. Just as I expected. As the real-world data trickles in after more than 2 years of ownership, it is becoming obvious that nobody knows anything with regard to the proper MO to extend the range/life of this battery.

The only interesting fact coming out of derkraut's car is that maybe it is ONLY the age of the battery and not how it's used that matters.

Still, I feel vindicated. Sorry for your loss, derkraut.

 

[Stoaty]

The only interesting fact coming out of derkraut's car is that maybe it is ONLY the age of the battery and not how it's used that matters.

No, it is the age of the battery, the number of full charge-discharge cycles, time the Leaf is parked in the sun, and most importantly, the climate. Charging to 100% appears to be a fairly minor factor, assuming the car doesn't sit at full charge in a hot climate for a long time.

 

[DaveEV]

I am sorry to hear you lost a bar. I too have lost a bar. It appears that time (age) is the dominant factor in capacity loss. I lost my first bar also at 2 1/2 years. I was upset when it happened as I babied my Leaf like you do and live in cool San Diego.

Yeah, looks like all San Diego LEAFs lose their first bar around 2.5 years if you drive a fairly normal amount of miles.

It looks like we're going to start seeing the 2nd bar go away for us early LEAFers around the 3.5 year mark - quite a bit earlier than the 5 years Nissan told us to expect on average.

 

[surfingslovak]

I was surprised to note that I lost my first capacity bar today @ 15,600 miles on my 2011 SLE.

Sorry to hear! What would be your long-term energy economy? Any idea? It looks like you are driving about 6,300 miles annually. Is that about right? Do you take your LEAF out of the garage regularly? I'm trying to determine how much it might be sitting in the sun on a weekly basis.

A preliminary result from Stoaty's model says that about 3/4 of the capacity loss seen in San Diego after 15,600 miles and 2 1/2 years of ownership is driven by calendar aging. The model predicts 13.66% loss using your mileage, some assumptions and a generic set of temperature data from San Diego.

 

[surfingslovak]

2) Literature searches of long-term calendar battery degradation testing do not indicate a leveling off of capacity loss as the battery fades. Some testing indicates calendar degradation accelerates as the battery capacity degrades.
3) Battery testing often uses constant-SOC charge and discharge endpoints rather than constant-energy discharges as would tend to occur in an electric vehicle. This discrepancy between testing and actual use tends to make battery models optimistic. Previous discussion: 1, 2
6) The battery temperature management system on the LEAF functions like a track-and-hold for temperature. When you couple this fact with the fact that most LEAF drivers use the car to commute to work, returning home during the hottest part of the day, you end up with LEAF batteries experiencing an average temperature environment which is quite a bit warmer than the average climate where the LEAF is located. Previous discussions: 1, 2, 3, 4

I'm sorry, I didn't have time to review this synopsis until now. I've been operating under pretty tight time constraints all summer. That said, and for the sake of the discussion, I don't agree with the points I quoted above. As I said on multiple occasions, while I appreciate the attention to detail and the many contributions to this topic and the forum, I find it necessary to point out that things should be kept in proper context and perspective. Stoaty's model is based on less than a handful rather simple assumptions. I believe that the design goal was to deliberately keep things as simple as possible, focus on the largest contributing factors and then refine the model as necessary. While it would be great to have an idea how much exactly parking the LEAF in a garage with Western exposure adds to battery degradation, and what the relative contribution of 100% charging and daily quick charging was, given the current instrumentation and the average usage patterns, we will likely never learn.

While it's easy to point out certain shortcoming of battery test protocols, and the perceived deficiency of the battery temperature or battery voltage sensors, I believe that these are not major contributing factors to battery capacity loss. I think it's important to keep that in mind, and state that on record, since there are many new owners reading this board, and even some of the old-timers might not have a good grasp of the situation. It would be good to keep in mind that based on the field data collected over the last 2 1/2 or 3 years, battery capacity loss is predominantly driven by the prevailing average temperature at the place of residence. Yes, having a hotter garage than this average will accelerate capacity loss. And so will driving the car during the hottest part of the day, since the battery will heat up, and only slowly cool down. None of these factors are going to come close to the impact of the local climate in terms correlation to battery capacity loss.

Furthermore, while traditional battery cycling tests have their limitations, they are also stressing the battery more heavily than what you appear to portray above. My understanding is that a typical lithium-ion battery test charges the battery to its full potential of 4.2V and then discharges it to 2.5V, which is about as empty as it gets. This goes further than what the LEAF would the driver permit; it's more than filling to 100% and then turtling the LEAF on every single charge. Moreover, these tests are typically conducted at 1C charge rate, which comes close to the average QC speed. Think about it for a moment, who would do that to their car? Even a few times, and not hundreds or even thousands of times? It's easy to forget this perspective when pointing out that battery testing uses constant-SOC charge and discharge endpoints rather than constant-energy discharges. This also gives the less informed reader the wrong impression, and exaggerates the problems with battery testing and our ability to predict what will happen in the field.

What exactly is gained from a constant energy discharge? In my experience, battery tests use a constant load, which is a bit simplistic, but the load is often 1C for the sake of expediency. That's an equivalent of driving the LEAF 75 or 80 mph on the freeway, which should be a pretty harsh stress test. Cycling tests can take weeks and sometime perhaps months to complete, and there is not enough time to use lower charge and discharge rates.

And lastly, my research early on has indicated that the cathode material becomes more resistant to heat as it ages and slowly degrades. That may or may not be true, but that's what I saw. I will try to find this reference. Additionally, the standard formula for battery calendar aging is always based on square root of time, and I have provided at least one reputable reference for this type of modeling. While we might see more of a linear decline of capacity with the LEAF, it would be good to acknowledge that this type of modeling is typically approached this way. I recall that you (and perhaps others) brought up other literature references to capacity degradation accelerating over time and being worse than linear. While that's a possibility, I would be skeptical of assuming that upfront.

My suggestion would be to go with the most common approach, and then alter, if the field data indicates different progression of capacity loss. I think that going with a mainstream approach, and then adapting it to the specific situation observed with the LEAF is a reasonable approach.

 

[DaveEV]

The model predicts 13.66% loss using your mileage, some assumptions and a generic set of temperature data from San Diego.

derkraut lives in Rancho Penasquitos which is farther inland and certainly in an area which can easily be 5-10F hotter than downtown San Diego in the summer. Rancho Penasquitos is about 10 miles inland from the coast.

 

[RegGuheert]

I was surprised to note that I lost my first capacity bar today @ 15,600 miles on my 2011 SLE.

I'm sorry to hear about your loss of a bar. I'm posting to contrast our 2011 LEAF SL battery experience with yours.

I would contend that my car has been the most "babied" Leaf out there, to wit:

I've Never QC'd; I've never seen more than 6 battery temp bars; My car has never been located where the temperature exceeded 90 degrees (I live 6 miles from the beach in San Diego); I've never driven it to turtle, or even VLBW; I've charged to 100% less than a dozen times since new. About 90% of the time, my battery SOC is between 4-7 bars when not driven for several days. I've done 95%+ of my charging at night in my garage with my level 2 EVSE, using the car timer. My car is almost always in a cool (65-75 degrees) garage when not being driven. I drive in ECO 100% of the time.

You certainly have my vote for "Best Battery Babier"!

We baby our LEAF's battery in much the same way as you do, but it hasn't always been so. Here are a few differences:
- During the first six months of our LEAF's existence, it was a demo vehicle, likely sitting the entire time at 100% while being driven 2011 miles.
- For much of the first year of our ownership of the LEAF, it often sat at 80%. For the past year, we have kept it between 2 and 6 bars when sitting in the garage.
- While our LEAF has also never seen more than 6 battery temp bars and the ambient temperatures did not get above 90F much this year, it was exposed to over 100F in the summer of 2012.
- We charge to 100% about once per week, sometimes more often than that.

I'm technologically challenged, so I don't have any devices to measure battery capacity like a lot of you folks do. But, I'm surprised to have lost a bar with such low mileage.
Since my car is now 2 1/2 yrs old, I guess that time is just as detrimental (or more so?) than temperature, regarding battery degradation. I still intend to drive this car for at least another 5 yrs on my original battery. Of course, not having to commute (did that for 35+yrs) gives me lots of options.

So, let me summarize your situation:

Model: 2011 LEAF SLE
Manufactured: Apr 2011?
Serial Number: 4248
Purchased: June 2011
Miles: 15,600
Garaged in: San Diego, CA
Current Battery Capacity: ~55.25 Ah

For comparison here is the same information for our LEAF:

Model: 2011 LEAF SL
Manufactured: June 2011?
Serial Number: 5926
Purchased: March 2012
Miles: 14,600
Garaged in: Winchester, VA
Current Battery Capacity: ~59.25 Ah

If we assume the batteries start life with around ~66.25 Ah of capacity (big assumption!), we come to the conclusion that derkraut's LEAF has lost about 57% more capacity than our LEAF. So, what can account for these differences? Here are a few things:

Miles: 15,600 versus 14,600 miles
Age: 30 versus 28 months since manufacture
Climate: San Diego, CA versus Winchester, VA.

Using Stoaty's Battery Aging Model (v0.83 since I don't have a newer one for Excel), I get the following predictions:

derkraut: 11.15% (Compared with 16.6% reported by car.)
RegGuheert: 10.21% (Compared with 10.56% reported by car.)

(Stoaty: Can you please provide this comparison in the latest version of your model?)

drees has pointed out one possible factor which could explain the difference:

The model predicts 13.66% loss using your mileage, some assumptions and a generic set of temperature data from San Diego.

derkraut lives in Rancho Penasquitos which is farther inland and certainly in an area which can easily be 5-10F hotter than downtown San Diego in the summer. Rancho Penasquitos is about 10 miles inland from the coast.

I suppose there could be some error due to the fact that while derkraut's BMS has had the P3227 reprogramming, ours has not. But, frankly, I don't think that is a significant factor. Once our BMS is reprogrammed, I guess we will find out how much difference it makes on our LEAF. (And perhaps this is why some have reported what looks like accelerated degradation after receiving the reprogramming...)

In any case, our BMS is reporting degradation very close to what Stoaty's latest model predicts, which derkraut's BMS reports about 50% more degradation than Stoaty's (old) model predicts.

So what other factors could cause derkraut's babied LEAF to lose capacity quite a bit faster than any of the predictions out there?

 

[derkraut]

I was surprised to note that I lost my first capacity bar today @ 15,600 miles on my 2011 SLE.

Sorry to hear! What would be your long-term energy economy? Any idea? It looks like you are driving about 6,300 miles annually. Is that about right? Do you take your LEAF out of the garage regularly? I'm trying to determine how much it might be sitting in the sun on a weekly basis.

A preliminary result from Stoaty's model says that about 3/4 of the capacity loss seen in San Diego after 15,600 miles and 2 1/2 years of ownership is driven by calendar aging. The model predicts 13.66% loss using your mileage, some assumptions and a generic set of temperature data from San Diego.

To answer slovak's questions: My long-term energy economy since purchase (carwings) is 4.6. Yes, I've been averaging about 20-25 miles a day or so, and I charge to 80% an average of 2-3 times per week. My Leaf is ALWAYS in the garage when not driven. I can see where I'll have to start charging to 100% for my occasional 50 mi round trip, playing taxi for my grand daughter.

 

[stanley]

I lost my first bar after 27,000 miles. My outside temperature is on average about 3-5 degrees cooler than Derkraut's location. About 3-4 miles from the Coast. The car virtually never sits in the sun. Always in the garage when not in use. Garage is always between 62 and 72 degrees.

 

[stanley]

I love the car but I am not happy with Nissan. The degrading is more than originally promised when I leased the car. With a 15 to 20% loss of range, range is beginning to be a challenge. Oh well, I only have 6 months to manage the problem before I turn the car in. Unless Nissan's 2014 model adds an optional battery pack(more than 24) I will be moving on to another EV brand

 

[Stoaty]

Using Stoaty's Battery Aging Model (v0.83 since I don't have a newer one for Excel), I get the following predictions:

derkraut: 11.15% (Compared with 16.6% reported by car.)
RegGuheert: 10.21% (Compared with 10.56% reported by car.)

(Stoaty: Can you please provide this comparison in the latest version of your model?)

No, but I can do the next best thing: Wiki now contains links to Excel versions of the model, one (XLS) for Microsoft Excel 2007 and earlier, one (XLSX) for Microsoft Excel 2010 and later. Both are courtesy of TomT. All earlier versions of the model should be discarded.

http://www.mynissanleaf.com/wiki/index.php?title=Battery_Capacity_Loss#Battery_Aging_Model" onclick="window.open(this.href);return false;

 

[surfingslovak]

derkraut lives in Rancho Penasquitos which is farther inland and certainly in an area which can easily be 5-10F hotter than downtown San Diego in the summer. Rancho Penasquitos is about 10 miles inland from the coast.

Thank you drees! I pulled up the temperature profile for both locations on weatherspark.com, and it seems that Rancho Penasquitos certainly experiences higher temperatures than what they have listed for San Diego. Perhaps this will bring Stoaty's model closer in line with the actual loss experienced by derkraut.


Rancho Penasquitos

San Diego

 

[surfingslovak]

To answer slovak's questions: My long-term energy economy since purchase (carwings) is 4.6. Yes, I've been averaging about 20-25 miles a day or so, and I charge to 80% an average of 2-3 times per week. My Leaf is ALWAYS in the garage when not driven. I can see where I'll have to start charging to 100% for my occasional 50 mi round trip, playing taxi for my grand daughter.

Thank you for that. I downloaded the latest Excel version of the model Stoaty has provided, corrected the average energy economy and reduced the amount of time the car spends sitting in the sun to a total of 2 days per week, which hopefully properly reflects the amount of driving you do with the LEAF. The predicted loss is now 13.06%. Looking at the temperature profile for Rancho Penasquitos, it appears that if we computed the effective temperature for that location, Stoaty's model would return a higher loss, which would be closer in line with the capacity bar loss you just experienced.

 

[RegGuheert]

No, but I can do the next best thing: Wiki now contains links to Excel versions of the model, one (XLS) for Microsoft Excel 2007 and earlier, one (XLSX) for Microsoft Excel 2010 and later. Both are courtesy of TomT. All earlier versions of the model should be discarded.

http://www.mynissanleaf.com/wiki/index.php?title=Battery_Capacity_Loss#Battery_Aging_Model" onclick="window.open(this.href);return false;

Awesome! Thanks!

Here are the corrected figures:

Using Stoaty's Battery Aging Model v1.00, XLS format, I get the following predictions:

derkraut: 12.52% (Compared with 16.6% reported by car.) (This differs from Slovak's number since I used 0 days in the sun.)
RegGuheert: 11.35% (Compared with 10.56% reported by car.) (Also 0 days in the sun per week.)

So derkraut's car exhibits 33% more capacity loss than predicted (or 27% using Slovak's numbers), while mine is pretty much dead on. (Nice job, Stoaty!) It seems like derkraut's LEAF battery is a bit of an outlier in the bad direction.

I wonder if only charging to 100% very infrequently can cause imbalances which can lead the BMS to believe the battery capacity is lower than it really is. It's really hard to know...

 

[Stoaty]

derkraut lives in Rancho Penasquitos which is farther inland and certainly in an area which can easily be 5-10F hotter than downtown San Diego in the summer. Rancho Penasquitos is about 10 miles inland from the coast.

Thank you drees! I pulled up the temperature profile for both locations on weatherspark.com, and it seems that Rancho Penasquitos certainly experiences higher temperatures than what they have listed for San Diego. Perhaps this will bring Stoaty's model closer in line with the actual loss experienced by derkraut.

If I get the energy in the next couple of months, the next plan for the model would be to add more cities. There are a lot of variables that can affect how well the model predicts an individuals battery capacity loss, but as always, climate is the main one. Having more geographic locations would help significantly.

Note to Reg: I suspect that the proper temperature profile would put the prediction closer to what derkraut has actually had.

 

[surfingslovak]

So derkraut's car exhibits 33% more capacity loss than predicted (or 27% using Slovak's numbers), while mine is pretty much dead on. (Nice job, Stoaty!) It seems like derkraut's LEAF battery is a bit of an outlier in the bad direction.

We don't know the exact effect derkraut's garage has on long-term average battery temperature. It likely raises the floor a bit, since it won't get as cold as ambient in winter. Likewise, it likely cuts off the tops, since it won't get as hot as ambient. Overall, the net effect could be zero, but it's a bit of an unknown here. Assuming that derkraut drives about 120 miles a week on average, and he prefers to do that during daylight hours, then the car is getting some exposure and experiences some solar loading. I think that budgeting one day or half a day a week would be appropriate. Unless of course, derkraut led the life of a vampire and shunned all sunlight. In that case, I think his house will be very popular on Halloween

 

[nosuchthing]

I wonder if only charging to 100% very infrequently can cause imbalances which can lead the BMS to believe the battery capacity is lower than it really is. It's really hard to know...

What I've been saying all along.

I lost my first at almost 40,000 (see below) in Marin (Novato). Max temps summer daytime are 90F. Mostly 80s otherwise. Not garaged, and yes, sunbaked on many occassions. One QC and 100% every night. Two turtles and many LBWs and a few VLBWs.

Where do I fit in in the above scheme?

 

[derkraut]

Well---I haven't charged to 100% in about 2 months or so. The reason for that is because Nissan says that 80% makes the battery last longer, eh? Maybe I should charge to 100% a few times, to "balance the pack"? At any rate, I am definitely losing range. today we went to church with 80% charge (showed 9 bars on departure). When we got home I was @ 5 bars. For the exact same trip in the past, we always got home with 6--sometimes--7 bars. Same roads, pretty much same OAT, same driver.

Oh wait! The preacher was extra long-winded today; maybe his hot air raised my battery temp?? :lol:

 

[DaveEV]

Well---I haven't charged to 100% in about 2 months or so. The reason for that is because Nissan says that 80% makes the battery last longer, eh? Maybe I should charge to 100% a few times, to "balance the pack"? At any rate, I am definitely losing range. today we went to church with 80% charge (showed 9 bars on departure). When we got home I was @ 5 bars. For the exact same trip in the past, we always got home with 6--sometimes--7 bars. Same roads, pretty much same OAT, same driver.

How many miles is that trip? I'm guessing about 25 miles?

I was getting 9-bar 80% charges all summer. It finally went back to 10-bar 80% charges about a week ago with the cooler weather. Pack is around 70F normally now.

Personally, I wouldn't bother trying to "balance the pack". It seems to take at least a few 100% charges to get it to do anything significant. If you get LEAF Spy you'll be able to see exactly how out of balance your pack is.

 

[dgpcolorado]

Personally, I wouldn't bother trying to "balance the pack". It seems to take at least a few 100% charges to get it to do anything significant. If you get LEAF Spy you'll be able to see exactly how out of balance your pack is.

I also don't see the point of balancing the pack. If you gain a Gid or two of capacity, is that really significant for most of us? Is there any other advantage to balancing?

[Because I have a bad cell-pair I try not to go much below VLBW for fear that it will shut me down early. But trying to balance the pack at "100%" does absolutely nothing for that cell-pair.]