Unfortunately, we have some troubling news: it appears that some of the 30 kWh Nissan Leaf battery packs are reportedly degrading at around three times the rate of the 24 kWh variant at 2 years of age.
Owners of over 640 electric and plug-in hybrid vehicles have signed up to our Flip The Fleet project to share data from their cars each month – it’s a “by EV owners, for future EV owners” effort to provide science-based evidence for the benefits and constraints of electric vehicles in New Zealand. So far, we have found mostly good news that will encourage other people to switch to electric, but the latest discovery of accelerated reported degradation of the 30 kWh Leaf batteries is potentially a serious problem for their owners, and one we must face and try to manage as soon as possible.
One of the statistics reported each month by many of the Nissan Leaf and e-NV200 van owners is “Battery State of Health” (SoH) – it’s a measure of the battery’s current capacity to store charge compared to its ideal, factory state. Another measure of the battery’s health is the number of “bars” which is displayed on the dashboard. Over the past three months, we have fielded an increasing number of queries by concerned 30 kWh Leaf owners who have noted a fall in SoH or bars. By January 2018, we were so concerned that we enlisted the help of several volunteers to shoulder tap owners to get more battery scans into the Flip the Fleet’s communal database. We were also gifted some battery scans collected by a concerned EV importer, who gathered these from various Leafs on auction floors in Japan. Dr. Daniel Myall, Flip the Fleet’s statistician, led the analysis of the data and, along with co-authors Dima Ivanov, Mark Nixon, Walter Larason and Henrik Moller, has just published the findings. We were also ably guided by the knowledge, experience and courage of a wider reference group of around 10 EV owners from throughout New Zealand, amongst whom we would particularly like to thank Donald Love and Joe Barnett. Joe and Donald guided the writing of the FAQs section below and did a lot of research to evaluate our results and their implications.
A picture paints a 1000 words: here’s one of the diagrams from the science report just published:
Figure 1 from the science report: All individual battery SoH measurements as a function of age with average 2nd-degree polynomial fits for both 24 kWh and 30 kWh Leaf models. Nissan’s estimate for expected average decline is 80% SoH after 5 years (Nissan, 2012; Nissan, 2017) and is shown by a red dot. There was large variability between cars, but both battery models showed increasing decline with age.
The full science report can be downloaded from https://www.preprints.org/manuscript/201803.0122/v1 or by clicking the button below:
Download science report
We alerted Nissan to our preliminary findings in January 2018, and then sent them the final draft of the science report for review on 23 February 2018. We have not heard back from them, and we are hopeful that Nissan will now choose to comment on the science report as part of the creative commons and open source peer review process.
In case you don’t want to wade through all the detail of the science paper itself, we have extracted the main points in the next section below. After that you’ll find a Frequently Asked Questions (FAQ) section where you can explore what all this might mean for you:
Key findings by Flip the Fleet about the observed 30 kWh Leaf battery degradation:
- There are over 3,250 Nissan Leafs registered in New Zealand. While most are 24 kWh, there are approximately 600 30 kWh Leafs already on the road. Based on Trade Me listings, we estimate that at least another 180 30 kWh Leafs are either in transit or awaiting sale on dealer yards. For context, there were 5,022 new and used light electric vehicles registered in NZ as at the end of February 2018 (including a few hundred smaller Paxters used by NZ Post, which we don’t count towards this calculation), meaning the 30kWh Leafs make up an estimated 14% of this fleet.
- Reported battery health (capacity to hold charge) at two years of age was estimated to be declining approximately 3 times faster on average in 30 kWh Leaf battery packs than for 24 kWh Leafs.
- The reported rate of decline in 30 kWh batteries observed so far is accelerating as the cars get older.
- We have not yet tested sufficient vehicles to check that the reduction in reported battery health accurately measures reduction in maximum range of the vehicle on a single charge. Nevertheless, we believe that there is no reason to expect that the reported battery health does not broadly indicate an upper limit for the range of the vehicle.
- We cannot see any reason to believe that the accelerated rate of degradation observed in reported battery capacity so far will not continue in the near future at least.
- The oldest of these 30 kWh Leafs are now approximately 2.3 years old. There is no scientific way of predicting accurately how well they will last in the long term.
- The observed decline in reported battery health for 24 kWh Leaf batteries at 5 years is close to what Nissan estimated it to be. The observed decline so far in many 30 kWh Leaf batteries, at an age of less than 2.3 years, is already close to where Nissan estimated them to reach at 5 years of age.
- We do not know for certain what the underlying causes of the observed rapid decline are, but our working hypothesis is that it relates to greater degradation at elevated temperatures and higher states of charge of the batteries.
- Nissan guidelines advise against repeated rapid charges on long trips – it may be that some owners do not realise this and thus do not use their car within these guidelines. There is evidence in our data that reported battery health had degraded very slightly more in Leafs that used more rapid charging per distance travelled, but this effect does not appear to be isolated to 30 kWh models. Therefore, successive rapid charging on long trips by itself does not appear to be a sufficient explanation for the rapid decline that we observed in 30 KWh vehicles, when compared against their 24 kWh counterparts.
- If the high rate of decline in battery capacity that we observed in the first 2.3 years of a 30 kWh Leaf’s lifetime was to continue, the financial and environmental benefits of this model are likely to be significantly eroded.
- None of the findings negate that the Nissan Leafs, even the 30 kWh model, may be an excellent choice for specific owner’s needs, especially for local travel. However, the additional prices currently paid for the 30 kWh model may adversely distort its value proposition depending on future battery health and its potential need for multiple replacements.
- We advise all buyers of any EV model to always get a battery scan check before purchase, where possible. Caution is required with Nissan Leafs, however, as the battery health metric can sometimes have a sharp drop following purchase depending on how the car was treated prior to sale and during transport to NZ, assuming this car is a second hand import. As reported to us, the battery health metric can also fluctuate by up to 8% once on the road in New Zealand following rapid charging on long road trips and has some variation with season, sometimes reducing sharply during cooler weather.
- Tracking what happens in the future is an important priority for EV owners and businesses. Flip the Fleet will continue to monitor and report rates of change of battery health, and to research why the observed changes are happening. To do this more effectively, we invite all of NZ’s EV owners to sign-up to Flip the Fleet to report their monthly statistics. It’s free, takes 10 minutes a month max. Visit www.flipthefleet.org and signup if you wish to help.
The accelerated decline observed so far by Flip the Fleet is isolated to one variant of one EV model. It does not signal general concern for the practicality, financial and environmental benefits of all EVs.
Frequently Asked Questions:
Daniel Myall, Walter Larason, Mark Nixon, Dima Ivanov, Joe Barnett, Donald Love and Henrik Moller.
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