Capacity Loss on 2011-2012 LEAFs

[edatoakrun]

Ernie Hernandez is making the gargantuan effort of trying to extract some pertinent information from the thousands of posts on this subject, and posting a summary at his blog:


http://livingleaf.info/2012/07/nissan-leaf-battery-capacity-loss-first-in-a-series/#comments" onclick="window.open(this.href);return false;

A look at how it all started

On May 9, 2012, a woman from Phoenix, Arizona posted on the My Nissan LEAF (MNL) forum that her car had lost one battery capacity segment. The battery capacity level gauge is made of of 12 segments – 10 white bars and 2 red bars...


This owner had indicated that she had owned the car for 14 months, and had accumulated 17,000 miles in that time. In response to questions regarding her charging behavior, later that day she posted the following:

* We always charge to 100%
* We do ‘top it off’ a lot.
* The car sat at 100% for a month in May, 2011, not plugged in.

Referring back to our previous article regarding the Care and feeding of the Nissan LEAF battery, all three of these behaviors are cautioned against. When combined with the Phoenix heat, these could be contributing factors to the battery capacity loss experienced by this particular LEAF.

Four days later, on May 13, another forum member, also in the Phoenix area, posted the loss of their first segment at the one year of ownership mark. Not a particularly high mileage car, with just over 13,600 miles driven in the first year, but this LEAF was also charged to 100% every night. The owner also reported that the car had never been quick charged.

Five days after that another report came in of a lost segment, also in Phoenix. Just a few days prior he had posted his charging habits as follows:

Initially, always to 100% charge, starting at 9:00 PM. (Why is the start time important? Because according to this owner, sometimes the charge would be completed by 11:00 PM and it could be sitting with a 100% charge for eight hours or more each night.) Two weeks ago he changed the timer to provide 100% charge ending at 4:00 AM to reduce the amount of time at 100%. Delivery was taken in early February 2011, so the car may have been sitting with a 100% charge for roughly four months of the last year (eight hours per day times twelve months) . If sometimes the charge was completed in early morning instead of late the prior evening, it could be less total time at 100%, but still a sizeable chunk of time. Also, this owner tended to top off to 100% from short trips.

On May 20, two days later, a fellow Arizona LEAF owner (an electrical engineer) reported losing his first battery capacity segment. Not in Phoenix, but in another extremely hot part of Arizona. How do we know this? Because this owner has posted a Google doc spreadsheet dating back to August of 2011 with his vehicle information, ambient temperature, mileage, and pretty much anything else that he felt like keeping track of. He took delivery of his car at the end of May 2011. He lost his first battery capacity segment just shy of one year later with just over 14,100 miles on the clock. His immaculate records show that he also charged to 100% on a regular basis with several “topped off” comments in the comment section.

Finally, on that same day, another Phoenix LEAF owner posted of the loss of his first battery capacity segment. This is a relatively high mileage LEAF (16,500 miles in less than a year). One difference to the pattern here is that this owner charges to 80% typically, with only about a dozen 100% charge sessions over the past year.

While we have a lot of reading yet to do, it is clear that there is a clear pattern in four of these five vehicles. Consistent charging to 100%, with the battery charge topped off after short drives. In addition to the extremely high heat of Arizona last summer, these could possibly be contributing factors to the battery capacity loss...

 

[DaveinOlyWA]

Anybody have an explanation for the relatively constant ~393 V reports, at varying levels of kWh capacity?

P=watts= voltage squared/resistance or P= V2/R or PR=V2. in this relationship. if V remains constant and kw (P) goes down, R must go up. this happens when pack cools

 

[edatoakrun]

Anybody have an explanation for the relatively constant ~393 V reports, at varying levels of kWh capacity?

P=watts= voltage squared/resistance or P= V2/R or PR=V2. in this relationship. if V remains constant and kw (P) goes down, R must go up. this happens when pack cools

Yes, but TikTock's kWh went up, concurrent with seasonally colder battery temperatures.

Wouldn't a temperature-induced R increase tend to indicate his battery capacity actually increased even more than the ~8% he reported last winter?

 

[GaslessInSeattle]

the IRS did not require proof that we owned the car through the tax year to collect the rebate. We sold our 2011 before filing, though it was Feb of 2012. I believe there is no time limit technically on how long you need to own the car to get the credit, it just can't be purchased in order to resell, as in such things as dealers can't buy the car in order to collect the rebate and resell. If you bought the car with the intention of keeping, I don't see an issue but certainly there are no guarantees with the IRS, they did take their sweet time to get our rebate to us. I see nothing stopping people from selling a car within the year they bought it due to unforeseen circumstances, like undisclosed battery limitations, and collecting the rebate. The credit is there in part to help buffer such risk.

I really hope alarm bells are sounding at Nissan, it's clear the natives are getting wrestles, Nissan's next move could make or break the Leaf as a viable mass market car.

So, If I were to contemplate selling my car now (9 months of ownership), what tax "rebate" liabilities would I owe? IIRC, the CA state will want their $2500 back if you sell prior to 2 years of ownership. But, what about the $7500 from the feds, any strings on that one?

Actually, I think CA wants a prorated return if you sell or move out of state within three years. The federal $7500 is not a rebate, but a credit. Once they give it to you, it's yours, but that can't be until after the end of the tax year when you buy the car. They don't care what you do with the car after that tax year. That means no reduction in your credit unless you have an unusual tax calendar, even if they haven't admitted yet that they owe you the money. If you were to buy and sell within the same tax year you might have trouble claiming it.

Ray

 

[Stoaty]

Ernie Hernandez is making the gargantuan effort of trying to extract some pertinent information from the thousands of posts on this subject, and posting a summary at his blog:

http://livingleaf.info/2012/07/nissan-leaf-battery-capacity-loss-first-in-a-series/#comments" onclick="window.open(this.href);return false;

Outstanding summary of the data on earliest reported Leaf battery capacity loss. Looking forward to the sequels.

 

[GaslessInSeattle]

There was no penalty for us, but that may have been because we signed the new leaf up right away and resigned a contract, which is now 3 years. if it comes to selling, it will be interesting to see what the consequences are, because this time, it's unlikely we will be trading up to a new Leaf and frankly at this point, there just isn't another attractive BEV with Quick Charging.

So, If I were to contemplate selling my car now (9 months of ownership), what tax "rebate" liabilities would I owe? IIRC, the CA state will want their $2500 back if you sell prior to 2 years of ownership. But, what about the $7500 from the feds, any strings on that one?

Actually, I think CA wants a prorated return if you sell or move out of state within three years. The federal $7500 is not a rebate, but a credit. Once they give it to you, it's yours, but that can't be until after the end of the tax year when you buy the car. They don't care what you do with the car after that tax year. That means no reduction in your credit unless you have an unusual tax calendar, even if they haven't admitted yet that they owe you the money. If you were to buy and sell within the same tax year you might have trouble claiming it.

Ray

I also believe EVProject participants that received quick charge ports in their LEAF's at no extra cost and an EV Project supplied EVSE have agreed to stay in the program until the end of 2012. After which I believe there is no more commitment from the consumer. Not sure what the penalty is for dropping out early, I would imagine they'd examine the circumstances.

 

[DaveinOlyWA]

You said it yourself. It changed with the weather. The BMS is probably spoofing the voltage hen it senses the temp is too high for safe charging. Just like I lose 2+ kw capacity in winter due to cold weather, u also lose some due to heat. Some is permanent some I am guessing is not

Anybody have an explanation for the relatively constant ~393 V reports, at varying levels of kWh capacity?

P=watts= voltage squared/resistance or P= V2/R or PR=V2. in this relationship. if V remains constant and kw (P) goes down, R must go up. this happens when pack cools

Yes, but TikTock's kWh went up, concurrent with seasonally colder battery temperatures.

Wouldn't a temperature-induced R increase tend to indicate his battery capacity actually increased even more than the ~8% he reported last winter?

 

[edatoakrun]

="DaveinOlyWA"]...The BMS is probably spoofing the voltage hen it senses the temp is too high for safe charging. Just like I lose 2+ kw capacity in winter due to cold weather, u also lose some due to heat. Some is permanent some I am guessing is not

Well, if TickTock's reports of cold-season increased battery capacity are confirmed by others, I don't see how it could still be a "guess", that some significant proportion of "lost" battery capacity is temporary, and not "lost" at all.

What is guesswork at this point, IMO, is the majority of hysterical and FUD posts on this and other threads, extrapolating the limited number of capacity bar disappearances, as evidence of rapid battery degradation, and a catastrophic failure By Nissan.

 

[DaveinOlyWA]

I actually dont feel that. I feel thatmaybe 5-10% at the most is temporary

 

[surfingslovak]

What is guesswork at this point, IMO, is the majority of hysterical and FUD posts on this and other threads, extrapolating the limited number of capacity bar disappearances, as evidence of rapid battery degradation, and a catastrophic failure By Nissan.

Hold your horses please. We discussed seasonal effects on Gid readings last summer already. Were you there? Although it's prudent to assume that some of the capacity loss is temporary, I believe that Nissan has their work cut out for them and plenty explaining to do.

 

[mdh]

Here is my theory (sorry if this is a repeat as I had a PC problem)

1. Nissan's passive TMS has some guard bands that are dynamically adjusted based on extreme temperatures (operating, charging, environmental, ...) for battery protection
2. It has a form of machine learning technology that is trained/learned by a number of operating and environmental factors.
3. The TMS did not adjust/learn fast enough to the extreme heat in Az to expand the guard bands within the battery (dynamically reducing capacity)
4. The heat might have been magnified by the ultra hot pavement in Az

As a result, the batteries were damaged. I recall Mark Perry and Nissan's Chief Leaf Eng tell us the car will protect you from you during their visit to the Bayleaf owners meeting.

Ok, maybe my silicon valley software imagination has gotten the best of me. I don't believe Nissan knew about any problems before they shipped. I think this boils down to a software problem with their TMS.

Please be gentle, but wanted to share my thoughts

 

[RegGuheert]

What is guesswork at this point, IMO, is the majority of hysterical and FUD posts on this and other threads, extrapolating the limited number of capacity bar disappearances, as evidence of rapid battery degradation, and a catastrophic failure By Nissan.

Well, these "hysterical and FUD posts" are only based on what Nissan says those bars mean. No one here made that stuff up. In addition, the service manual states that the capacity bars are not affected by temperature.

I agree that may not be exactly true, but if that is the case, all Nissan has to do to clear up the confusion would be to communicate what the bars *really* mean. Until they do that, we are left with the face value of their statements and deciding how to interpret the words and charts and what we believe and don't believe.

 

[TonyWilliams]

I recall Mark Perry and Nissan's Chief Leaf Eng tell us the car will protect you from you during their visit to the Bayleaf owners meeting.

Folks, Nissan / Mark Perry / et al, will never say that they will NOT take care of you. It costs them NOTHING to say that, and would be stupid to not provide you positive lip service.

Actual action (that costs Nissan big bucks) is less likely.

I don't quite follow your software argument. Sure, there may be an issue there, but it has become quite clear that lithium batteries in 120F-140F temperatures in a parking lot (that's without quick charging or otherwise heating the battery from use) seem to be the extremely obvious problem that no magic software will fix. Every other manufacturer uses a TMS, even the cheaper Mitsubishi car.

Nissan chose to chance it. It was a bad gamble.

 

[DaveEV]

Access to a fraction of the “top” of the battery capacity has been restricted, presumably to prevent the battery degradation that would result from this abuse.

Since we have no reason to believe that the reported battery voltage is wrong - I have to wonder if it's limiting access to the bottom of the pack.

To do this, we'd need to collect battery voltage at known points at the opposite end - at least LBW and preferably VLBW and even turtle. Ideally, you'd stop the car as soon as possible after one of these warnings, let the battery rest some time and record the voltage, ambient temperature, number of battery temp bars and GID count.

To my knowledge we don't have any data like this, but this would identify if the BMS is hiding any additional capacity at the bottom of the pack.

 

[RegGuheert]

To my knowledge we don't have any data like this, but this would identify if the BMS is hiding any additional capacity at the bottom of the pack.

TickTock has recorded voltages at a bunch of low GID values over time. They don't correspond to LBW or VLBW, but a plot of GIDs versus voltage might tell us something about how these are related, particularly if we could tag the temperature at each point.

 

[surfingslovak]

To do this, we'd need to collect battery voltage at known points at the opposite end - at least LBW and preferably VLBW and even turtle.

The turtle cutoff seems to be 3.2 V on the cell level or about 308 V on the pack level. I watched it several times, but don't have any recordings.

To do this, we'd need to collect battery voltage at known points at the opposite end - at least LBW and preferably VLBW and even turtle. Ideally, you'd stop the car as soon as possible after one of these warnings, let the battery rest some time and record the voltage, ambient temperature, number of battery temp bars and GID count.

To my knowledge we don't have any data like this, but this would identify if the BMS is hiding any additional capacity at the bottom of the pack

Agreed, it would be nice to have all this data. Is it safe to assume that you have seen the voltage plot TickTock did last October?

Click to open

 

[Stoaty]

Here is my theory (sorry if this is a repeat as I had a PC problem)

1. Nissan's passive TMS has some guard bands that are dynamically adjusted based on extreme temperatures (operating, charging, environmental, ...) for battery protection
2. It has a form of machine learning technology that is trained/learned by a number of operating and environmental factors.
3. The TMS did not adjust/learn fast enough to the extreme heat in Az to expand the guard bands within the battery (dynamically reducing capacity)
4. The heat might have been magnified by the ultra hot pavement in Az

As a result, the batteries were damaged.

That's a very imaginative theory. Not saying that is good or bad, but I think you should get points for the sophistication of your theory.

 

[jspearman]

How many Arizona cars on the forum still have 12 bars? Maybe this question has been asked before, and if so, my apologies.

 

[aqn]

My recent energy economy is identical to my long term average, perhaps even a bit higher:

Lifetime average (dash) - 5.7
Center console reading (reset a couple of months ago and not touched since) - 5.9

5.9?!!! What, you push your LEAF around?!

 

[Stoaty]

My recent energy economy is identical to my long term average, perhaps even a bit higher:

Lifetime average (dash) - 5.7
Center console reading (reset a couple of months ago and not touched since) - 5.9

5.9?!!! What, you push your LEAF around?!

No, but when it is windy I have a sail that I raise to take advantage of "wind power". You have heard of the "Clipper Leaf"?