Nissan publishes open letter to Leaf owners over battery capacity loss
Yesterday was National Plug-in Day (NPID), a nationwide celebration of electric vehicles organized by Plug-in America, the Electric Auto Association and the Sierra Club. On the eve of NPID, or more succinctly, on the eve of thousands of Nissan Leaf owners gathering face-face across the country, Nissan released an open letter concerning the battery capacity loss issue that is worrying Leaf owners. The latest letter is again an attempt to quell the fears of Leaf owners, but it appears that Leaf owners are starting to have a deaf ear for Nissan's communications on this matter.
The issue is that some Nissan Leaf owners are noticing diminished battery capacity. This lost capacity is measured in one of two ways: 1) when the Leaf is fully charged, the dashboard State of Charge will show fewer "bars" of capacity; 2) 3rd party instrumentation gauges which display battery charge in GID's. Diminished battery capacity generally means the Leaf has a shorter driving range, making it less useful as a car. Primarily the affected Leaf's are in hot climates like the Phoenix area, leading many to think the cause of battery capacity loss is the heat and blaming Nissan's choice to not have a cooling system. Nissan, in their responses in June, last week, and below, are focusing on the Phoenix and Arizona based Leaf owners. Not liking Nissan's responses, a large group of Nissan Leaf owners staged a massive test of Leaf battery capacity in Phoenix a bit over a week ago, and managed to measure some of the capacity loss. In the meantime, Coda Automotive is making the case for the thermal management system their engineers chose to use.
Nissan's latest letter (replicated below) reveals more about the company's investigation than had been revealed last week, but "more" is a relative term because there are many details left wanting.
When Nissan says "You are truly our best ambassadors to the next generation of passionate EV drivers," we should think back to July when it was beginning to sink in that Nissan Leaf sales this year were starting to be dismal. At that time loyal Leaf owners were brainstorming Nissan Leaf marketing ideas on the MyNissanLeaf forum. Today the MNL forum has a lot of worry about this battery capacity loss issue.
When Nissan says they identified seven Leaf owners in Phoenix, do we know for sure the issue is this limited? Browsing the MNL forum, there are many who do not live in hot climates who are suffering from diminished battery capacity. An example is Tony Williams who drove on the BC2BC trip (Baja California to British Columbia) in June, but there are others. The NPID event I attended in Silicon Valley had more than one person reporting diminished battery pack capacity. While these people have put a lot of miles on their Leaf's, Silicon Valley has neither hot nor cold weather.
Nissan says they "measured capacity, and conducted voltage testing on individual battery cells" which sounds nice, but what does it mean. Having built battery packs for electric motorcycles and cars, I can say that this cannot be done just by measuring the voltage of the battery pack and cells. Instead this test has to be a dynamic measurement over time, because lithium battery cells have largely the same voltage except when fully charged and fully discharged . To perform this test, Nissan's engineers will have had to completely charge and discharge each pack at least once to measure the amp-hours that can be pulled out, graphing the voltage the whole time.
Going by the discussion on MNL, Leaf owners are hearing Nissan say "nothing to see here, move along." What Nissan says in this letter is that the packs they tested are behaving as expected given the usage pattern of each individual vehicle. However, 2 years ago Nissan's promise in marketing literature was "80% remaining capacity after 5 years" without explaining nuances like the ambient temperature or the distance the car has been driven. It is a fair assumption for a Leaf owner to read "80% remaining capacity after 5 years" and think battery degradation will occur linearly over a set period of time. Nissan is trying to make the case, after the fact, in a way that looks suspicious to Leaf owners (going by discussion on MNL), that there are additional technical factors which were not disclosed to Leaf owners.
Indeed one of the MNL members suggested these disclosures by Nissan would help: 1. Produce an "ideal" speed/range chart that lets you know how fast/far you can travel on a single charge in a new car. All new cars should be able to match these numbers at a minimum. The data in NTB11-076a is not good enough, but it's a good start. 2. Provide guidelines on how capacity will be reduced over the warranty period based on where you live assuming typical usage (used as daily commuter, parked in sunny parking log, parked in garage, etc). 3. Provide guidelines on how tweaking usage habits may improve or reduce capacity loss over time. How does calendar life change when using 80% vs 100% charging? How does calendar life change when averaging 3.5 mi/kWh vs 4.5 mi/kWh?