Nissan Leaf DC fast charging testAs convenient as DC fast charging is, there have been lots of warnings that repeated dumping of so many electrons into an electric vehicle's battery pack in such a short time would reduce the battery's life. While everyone agrees that DC fast charging does have some effect on battery life, it may not be as bad as previously expected.

Over on SimanaitisSays, Dennis Simanaitis, writes about a recent presentation by Matt Shirk of the Idaho National Laboratory (INL) called DC Fast, Wireless, And Conductive Charging Evaluation Projects (PDF) that describes an ongoing test of four 2012 Nissan Leaf EVs that are being charged in two pairs of two. One pair only recharges from 50-kW DC fast chargers, which the other two sip from 3.3-kW Level 2 chargers exclusively. Otherwise, the cars are operated pretty much the same: climate is automatically set to 72 degrees, are driven on public roads around Phoenix, AZ and have the same set of dedicated drivers is rotated through the four cars.

"Degradation depends more on the miles traveled than on the nature of recharging."

What's most interesting are the charts on page seven of Shirk's presentation (click the image above to enlarge), which show the energy capacity of each of the four vehicles. When they were new, the four batteries were each tested to measure their energy capacity and given a 0 capacity loss baseline. They were then tested at 10,000, 20,000, 30,000 and 40,000 miles, and at each point, the DC-only EVs had roughly the same amount of battery loss as the Level 2 test subjects. The DC cars did lose a bit more at each test, but only around a 25-percent overall loss after 40k, compared to 23 percent for the Level 2 cars. Simanaitis' takeaway is that, "INL data suggest that the amount of degradation depends more on the miles traveled than on the nature of recharging." The tests are part of the INLs' Advanced Vehicle Testing Activity work and a final report is forthcoming.

These initial numbers from IPL do mesh with other research into DC fast charging, though. Mitsubishi said daily fast charging wouldn't really hurt the battery in the i-MiEV and MIT tests of a Fisker Karma battery showed just 10-percent loss over 1,500 rapid charge-discharge cycles.


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  • 47 Comments
      • 9 Months Ago
      What is a "Level 2 AC Charger" doing to recharge the batteries that differs from DC voltage input? To recharge a battery you have to apply a DC voltage to it to force the flow of electrons "backwards" through the battery. It does not matter what the input is, you have to convert it into a DC voltage just slightly higher than what the battery normally puts out on it's own, in order to force the battery to absorb, rather than discharge, power. I am forced to assume that a "Level 2 AC Charger" does two things that "High voltage DC Fast Chargers" don't do, in order to be more "friendly" to the batteries... 1) Match the input charging voltage to the current state of the battery a little better, 2) Go slower, to allow the battery to change internal chemical state less destructively. In short: The real difference is only the rate and power that the electrons are forced "backwards" through the battery. And if that's the case, there's no mystery, cramming more "hot electrons" through the battery faster is going to wear it out a little bit faster. It's good to know that the batteries are getting "tough enough" to not completely fry from this sort of treatment.
        Jeff
        • 9 Months Ago
        "Level 2" refers to 240V AC power being supplied to an on-board "charger" that converts it to the DC voltage that is needed to charge the battery. High voltage DC fast charging, as the name suggests, supplies high voltage DC power which can charge the battery faster. Since it's supplied as DC power, it can bypass the on-board AC/DC converter/charger and go (more-or-less) directly to the battery. And since it doesn't need to be converted from AC to DC, it can be done at much higher power levels. (In this instance, 50kW vs 3.3kW.)
      Joeviocoe
      • 9 Months Ago
      So the one thing that CAN be said from this study... is that Cycles (miles) have greater impact than Charging speeds. That being said, this study can NOT speak to the fact that Ambient temperatures and Calendar life are greater than Cycle life. Which is to say, that most Leafs will not likely follow the 'accelerated degradation over time' as this study shows... (*not until about 7 years, when calendar life starts to show*) Take a look at Stoaty's chart. Much more data, and and much more validation with actual cars on the road, in Phoenix and out of Phoenix. https://docs.google.com/spreadsheet/ccc?key=0AqhUVOciAXVhdEFId2ppVEViZmd0ckJxME95N0U4SUE&usp=sharing#gid=0
        Joeviocoe
        • 9 Months Ago
        @Joeviocoe
        http://www.electricvehiclewiki.com/?title=Battery_Capacity_Loss&oldid=2989 this too.
      Joeviocoe
      • 9 Months Ago
      I spoke to a Nissan Engineer this past weekend at the Bay Area's Alt-Car Expo He was speaking of some very exciting advancements for the next Leaf. ;)
        Joeviocoe
        • 9 Months Ago
        @Joeviocoe
        We talked mostly about the battery. I think the chemistry will change slightly to handle temperature variation with degradation better. Larger pack.
        Anderlan
        • 9 Months Ago
        @Joeviocoe
        You blue balling bastard. AND!?
        Jon
        • 9 Months Ago
        @Joeviocoe
        MY 2015? Does it include a face lift? Sorry, just really want to see a car that I would actually buy.
      Rotation
      • 9 Months Ago
      I'm not surprised, in my work with Li-Ions, by far the closest model is simply that the batteries don't like to be charged. And when you discharge them, that means you have to charge them again later, so basically it just means using them wears them out. I am distressed to see that I can expect to lose 6% of my capacity every 10,000 miles. That's insane. That makes a LEAF far more expensive to run than a gas car, despite the low cost of the electricity put in it. Battery chemistries better get a lot better.
        Cavaron
        • 9 Months Ago
        @Rotation
        Remember - it's not just the fast charging, they also run the cars in very hot Phoenix AZ. I would like to see a test like this in moderate climates.
          Rotation
          • 9 Months Ago
          @Cavaron
          I'd also like to see it in more temperate conditions. And in cold too. I want EVs for everyone, not just for NorCal climate.
          Joeviocoe
          • 9 Months Ago
          @Cavaron
          https://docs.google.com/spreadsheet/ccc?key=0AqhUVOciAXVhdEFId2ppVEViZmd0ckJxME95N0U4SUE&usp=sharing#gid=0 Best chart I've seen for the Leaf... and has been reported to be fairly accurate according to many owners.
        krona2k
        • 9 Months Ago
        @Rotation
        A LEAF in the states has done 100,000 miles with 15% loss. I'm not sure where that car is located. Average ambient temperature seems to be the most significant factor in LMO chemistry lifetime.
          BraveLil'Toaster
          • 9 Months Ago
          @krona2k
          The article says that these tests were conducted in Phoenix, AZ.
          krona2k
          • 9 Months Ago
          @krona2k
          Yes I know. I meant I don't know where the car that lost 15% after 100,000 miles was located. Somewhere much cooler I imagine!
      jack smith
      • 9 Months Ago
      The reason for this is because the Nissan Leaf and Chevy Volt both use Lithium Manganese chemistry batteries, not the standard Lithium-ion Cobalt. A standard Li-ion battery requires protection circuitry because it can only discharge at a rate of 1c, and sometimes 2C. These standard type batteries CAN NOT be over-charged or over-discharged, or else a thermal runaway event might very well occur. Dell laptops in the 90s famously exhibited this behavior. Lithium Manganese is different, it requires no protection circuitry because it is generally considered as a "safe chemistry" battery, meaning it is much less prone to such a thermal event. Lithium Manganese batteries generally can discharge at a rate of 10C without damage, and therefore charging one at a rate of 1C or even 2C should pose no particular problems. Since a Nissan Leaf battery is 24kWh, and this quick charger is operating at 50kWh, the C rate of charge would be roughly 2C for the Nissan's battery. However, I wouldn't suggest hooking up a Tesla Model S with it's Lithium Cobalt 85kWh battery to a 170kWh charger. While that would still be a charging rate of over 2C, very bad things will happen to the Tesla's battery if the protection circuitry is faulty and actually allows a 2C charge rate.
      Greg
      • 9 Months Ago
      After looking at that chart, I would have rephrased the title as "Slow Charging Doesn't Save Battery Life." Ouch, that's a lot of lost capacity. Reading the comments, though, is a bit reassuring. It's more likely that it's just AZ that's the problem.
      BipDBo
      • 9 Months Ago
      This study is really invalid because it was performed in Phoenix Arizona. The Leaf does not have a good battery cooling system, and they have had serious problems with Leaf batteries cooking in the area. Therefore, the amount of degradation due to quick charging looks a lot less significant because it is washed out by the great amount of degradation caused by the hot climate. 2% loss over only 40,000 miles will be significant as a car ages to over 100,000 miles. 2% is really unknown, however, because isolating charging speed caused degradation out of the much larger heat caused degradation is statistically irresponsible, especially given such a small sample size. Nonetheless, even in Arizona, 23%-25% over 40,000 miles is simply unacceptable, especially for a pure EV which does not have a range extender. What do you do as the car gets older, move closer to work? 40,000 miles is still a new car. If a new ICE car is properly maintained, it should easily reach 200,000 miles. My understanding is that one of the biggest factors that contribute to battery degradation is how often it is discharged to a very low level, and I think that topping the charge to 100% also can cause degradation. I think that there is a sweet spot, where if the battery is kept within a central charge level, around 20% to 90%, degradation is minimized. I don't think that the Volt has this problem because its battery isn't allowed to discharge to near the level that the Leaf battery is. The average Tesla S, with its much bigger battery is rarely discharged fully, so most of these probably won't have this problem.
        canuckinaz
        • 9 Months Ago
        @BipDBo
        Your claim that this study is "invalid" is completely wrong. All four cars experienced the same temperatures (and note that the study started in October and so didn't even experience the Phoenix summer), so the specific average temperature is less important than the type of usage. With the drives being essentially the same, that means that only the charging is different. Fast charging should cause more degradation in elevated temperatures, but this study is showing that the difference between DCFCs and AC L2s (at 3.3 kW at least) are minimal. Your "statistical analysis" leaves a lot to be desired. Just because there is a significant amount of degradation, the difference between the two charging regimes is not "washed out". If you were taking the difference as a percentage of the total degradation, you might have a case. But the difference itself is what matters, and the ambient temperature does not invalidate the study whatsoever.
          BipDBo
          • 9 Months Ago
          @canuckinaz
          They chose Phoenix because they live there.
          Joeviocoe
          • 9 Months Ago
          @canuckinaz
          yes, my point was that the study is not making such a conclusion, but people were looking at the graph and drawing a conclusion.
          BipDBo
          • 9 Months Ago
          @canuckinaz
          There was no breakdown of the individual sample measurements, which is only four cars, two control, two experimental. The small sample size is one reason it's invalid. And yes, the total degradation does matter and I'll tell you why. If the study took place in a milder climate, the total degradation would be lower. The degradation control cars (slow charging), average may be 5% so let's say that control A is 4% and control be is 6% 2% difference. In Arizona, with higher total degradation, the average is 23%, but the difference between the two would naturally diverge along with the total number. It would not be 22% and 24%. It would likely be more like 19% and 27%. This along with the small sample size, creates a larger statistical standard deviation and therefore larger standard error. A good researcher would make any attempts to eliminate other factors that would contribute to the measured result and cause more statistical deviation. The fact that the exact opposite was done in this study, to chose a location that would cause the greatest error, tells me that the researcher may have actually intentionally design a study that would show no statistical difference.
          Joeviocoe
          • 9 Months Ago
          @canuckinaz
          For the simple conclusion that, "mileage is greater than charging speeds" as a factor of battery capacity degradation... yes, this study is valid. However, since this study does not have a temperature control group... it is 'invalid' to come to any other conclusion... such as overall rate of degradation to be expected.
          canuckinaz
          • 9 Months Ago
          @canuckinaz
          INL isn't there--it's in Idaho. The specific researchers who performed the test are in Phoenix, but Idaho could have gone to other locations. You seem to have strong opinions on this study where none seem warranted. Your criticisms seem out of proportion as well.
          canuckinaz
          • 9 Months Ago
          @canuckinaz
          But does the DOE claim that this is the "end all-be all" of studies on it? No, it is simply testing four cars undergoing the same driving/charging cycles in the same climatic conditions. Of course in an ideal world, one would test many more cars. But as a taxpayer, do you want the DOE being profligate with your dollars? Your analysis still makes no sense. The location in a high-temperature locale should be the worst-case scenario for DC fast charging since it should cause more damage the hotter the ambient temperature is. The very fact that the degradation is not that much worse than the AC L2-caused degradation is indicative that DC fast charging has a smaller effect than expected. That is an important result. This is not in fact showing the "greatest error", it's showing that the effect is simply smaller than expected. You are criticizing the researchers without actually knowing why they chose the location they did. Maybe they were looking for that worse-case scenario--ever thought of that? A lot of posts on this blog are examples of people pontificating on topics about which they know very little. I think that your posts here are a prime example of this.
          canuckinaz
          • 9 Months Ago
          @canuckinaz
          @joeviocoe, first off, I don't see where any claims have been made about rates of degradation. The study presents the data from the four cars and that's it. But would you agree that a higher average ambient temperature should result in more degradation than a more temperate average ambient temperature? If so, the decision to host this study in AZ makes sense as it gives a worst-case scenario. I don't think that any conclusions on absolute degradation rates should be drawn from just four vehicles. But the fact that the fast charging did not result in significantly more degradation than 3.3 kW AC L2 charging is very interesting.
          canuckinaz
          • 9 Months Ago
          @canuckinaz
          I should note that I was mistaken that there was no Phoenix summer as part of the study. But the study has been all-year round, so only a portion of the study was during this hot time of year. But again, this doesn't matter. All of the vehicles are experiencing the same climatic conditions, and it's only the relative difference in degradation, not the absolute degradation, that is the key result here.
      mumbojumbo
      • 9 Months Ago
      If this data is accurate then it's disheartening to say the least. If a Leaf battery loses 25% of it's capacity after only 40,000 miles, then after extrapolating to 80,000 miles ones range would be roughly 45 miles on a fully charged battery. That's terrible. My current 35 mile round trip commute usually consumes the battery pack from full (reading about 90 miles) to 45 miles remaining range. So it required 45 miles of calculated range to go 35 miles, which would mean that at 80,000 miles I would be maxing out the batteries range. They would require replacement at that time. Maybe some of the other companies EV's with different chemistry or liquid cooled battery packs can get more extensive life from them. That's hopefully true or EV's will never gain popular acceptance due to battery degradation over such a short time.
        BraveLil'Toaster
        • 9 Months Ago
        @mumbojumbo
        It's worth noting these tests were done in Phoenix, the place that's the worst for the Leaf battery. I noticed that there was a big jump between 20,000 miles and 30,000 miles. One can come to the conclusion that those 10,000 miles happened during the summer. I recall that the guy who first exceeded his battery warranty lost less capacity than this. He lived in Washington state.
        Joeviocoe
        • 9 Months Ago
        @mumbojumbo
        Right... which is why you DO NOT EXTRAPOLATE in a linear way like you did. The degradation happens much faster from 100% - 75%... and much slower from 75% - 50%. And really, the Leaf battery is one of the worse for degradation right now. And they are likely changing that with the new Leaf 2.0
          Joeviocoe
          • 9 Months Ago
          @Joeviocoe
          Right, which is what I am saying. I disagree that the chart (and the conclusion of the article) is accurately portraying typical results. This article seems to focus on asserting that mileage has a much bigger impact on the pack, than charging. Which is fine... but the study doesn't have a 'control group' for moderate climate... but rather has all participants in the Hell of Arizona's desert. The heat soaking issue in Arizona could easily be the cause of this trend... because each summer day where the ambient temp is above 100 F, irreparably damages the cells. Basically... this study compares only two metrics (mileage and charging) while ignoring climate. So it is in no position to assert that other EVs would also follow an "accelerating degradation" profile, unless also in high temperature climates. This study should be re-done in a more neutral climate.
          Joeviocoe
          • 9 Months Ago
          @Joeviocoe
          Hmmm... it seems you may have something different going on. From what I have read on the MNL forums, and the Nissan engineer I spoke to this past weekend... the initial degradation is much faster.
          Joeviocoe
          • 9 Months Ago
          @Joeviocoe
          Look at Stoaty's infamous prediction chart. The MyNissanLeaf community really gathered a lot more data than this study. https://docs.google.com/spreadsheet/ccc?key=0AqhUVOciAXVhdEFId2ppVEViZmd0ckJxME95N0U4SUE&usp=sharing#gid=0 Change Annual miles to 12000. and change the city to Pheonix... on the INPUT tab Look at the PREDICTION tab.... Year to Year Increment loss Phoenix drivers experience a large drop in the first year, smaller drops in years 2 and 3... but then accelerate in degradation from there onward. Now, change to Boston. The degradation slows down, (until year 7, when calendar life becomes a bigger factor.) Similarly, moderate climates also show slower degradation through up until 7 years. http://www.electricvehiclewiki.com/File:Battery_Aging_Model_Graph.png
          Rotation
          • 9 Months Ago
          @Joeviocoe
          Not in my experience, Joeviocoe. In my experience, once you get past 20% capacity lost things start to move a lot faster. After about 65% it's kind of like falling off a cliff. Part of the problem is that not only does capacity go down, but internal impedance goes up, which means that under heavy loads the pack is less efficient with the capacity it has left.
          Joeviocoe
          • 9 Months Ago
          @Joeviocoe
          Did you make it to the Alt-Car expo in Richmond, btw?
          • 9 Months Ago
          @Joeviocoe
          If you look at the curve, you'll see that the battery start degrading quite faster after 20,000 miles, which implies something even worse than a linear extrapolation. Hopefully I'm wrong.
        aatheus
        • 9 Months Ago
        @mumbojumbo
        If your Leaf battery gets down that low, Nissan will replace it under the 5 year battery warranty. Unless you manage to go 60,000 miles in 5 years.
      • 9 Months Ago
      Why take chances on a early retirement of your Li-ion battery. Charge your EV with a level II charger that's powered by Hyper X high efficiency solar modules. Hyper X solar offers a better PTC to STC ratio "Real World" performance according to the California Energy Commission's performance rating listings than over 100 of SunPower's solar panel models. Hyper X solar also offers an incredible -0.27%/degree C temperature coefficient rating for awesome performance in hot/warm climates and best of all Hyper X solar systems are priced thousands less than a SunPower solar system.
      CoolWaters
      • 9 Months Ago
      Good to hear the batteries are more robust then thought.
        scraejtp
        • 9 Months Ago
        @CoolWaters
        I wouldn't consider 25% loss in 40k miles robust.
      2 wheeled menace
      • 9 Months Ago
      Entirely dependent on battery chemistry and C rate. There is absolutely no way that you can say something general about all batteries. I can charge my nanotech RC Lipo at >5C without it getting warm, but my panasonic 18650PDs get warm at 1/3rd of a C.
      Dave
      • 9 Months Ago
      So, even if they aren't fast charged, they lose ~22% of capacity after 40,000 miles?
        BipDBo
        • 9 Months Ago
        @Dave
        In Phoenix, AZ. Not in a more moderate climate. If you live somewhere as hot as Phoenix you probably shouldn't be an early EV adopter. You probably also should not do EV studies that don't relate to climate.
          GoodCheer
          • 9 Months Ago
          @BipDBo
          "The hypothesis is that fast charging will have larger effects in hotter climates." If that were the hypothesis, then they would have also had to test in cooler climates.
          canuckinaz
          • 9 Months Ago
          @BipDBo
          Goodcheer, Sure, that would be a good idea too. This is just one test.
          jeffwishart
          • 9 Months Ago
          @BipDBo
          BipDBo, the fact that it's hot in AZ is not necessarily a bad thing. The hypothesis is that fast charging will have larger effects in hotter climates. If this study is showing otherwise, then the choice of AZ is useful.
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