It's not quite as detailed as we hoped for, but at least Nissan is fully aware of the concern and is investigating the potential issue.
Earlier this week, we presented the highly detailed findings of an in-depth Nissan LEAF battery degradation study.
Battery Issues - Nissan LEAF 30-kWh Battery Degrades More Rapidly Than 24-kWh Pack
The takeaway from the published results were:
“At two years of age, the mean rate of decline of SoH of 30 kWh Leafs was 9.9% per annum (95% uncertainty interval of 8.7% to 11.1%; n = 82). This was around three times the rate of decline of 24 kWh Leafs which at two years averaged 3.1% per annum (95% uncertainty interval of 2.9% to 3.3%; n = 201).”
Or, in very simplified terms, the 30-kWh LEAF seemed to have much higher battery degradation rates than the 24-kWh LEAFs.
The study concluded by suggesting that the rate of decline in the 24-kWh version of the LEAF is acceptable, but suggests that the 30-kWh pack declines too rapidly to be considered within normal parameters.
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Following the release of the results of this study and our coverage of the potential issue, Green Car Reports reached out to Nissan for comment. EV communication manager, Jeff Wandell, offered this response:
“Nissan is aware that a limited number of customers have expressed concerns with the previous generation of the Nissan LEAF 30-kWh battery."
"LEAF owners are some of our most devoted customers."
"We take their concerns seriously, and have technical experts currently investigating the issues raised.”
We're glad to know that Nissan is looking into this potential issue. We'll report back if Nissan presents any additional information.
The abstract from the work titled “Accelerated Reported Battery Capacity Loss in 30 kWh Variants of the Nissan Leaf” contains more details on the issue. It states:
Analysis of 1382 measures of battery State of Health (SoH) from 283 Nissan Leafs (“Leaf/s”), manufactured between 2011 and 2017, has detected a faster rate of decline in this measure of energy-holding capacity for 30 kWh variants.
At two years of age, the mean rate of decline of SoH of 30 kWh Leafs was 9.9% per annum (95% uncertainty interval of 8.7% to 11.1%; n = 82). This was around three times the rate of decline of 24 kWh Leafs which at two years averaged 3.1% per annum (95% uncertainty interval of 2.9% to 3.3%; n = 201).
For both variants there was evidence for an increasing rate of decline as they aged, although this was much more pronounced in the 30 kWh Leafs. Higher use of rapid DC charging was associated with a small decrease in SoH. Additionally, while 24 kWh cars with greater distances travelled showed a higher SoH, in 30 kWh cars there was a reduction in SoH observed in cars that had travelled further.
The 30 kWh Leafs sourced from United Kingdom showed slower initial decline than those from Japan, but the rate of decline was similar at two years of age.
Improvements in the battery health diagnostics, continuous monitoring of battery temperatures and state of charge, and verification of a fundamental model of battery health are needed before causes and remedies for the observed decline can be pinpointed.
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 were to continue, the financial and environmental benefits of this model may be significantly eroded. Despite 30 kWh Leafs accounting for only 14% of all light battery electric vehicles registered for use on New Zealand roads at the end of February 2018, there is also the potential for the relatively poor performance of this specific model to undermine electric vehicle uptake more generally unless remedies can be found.
Myall, D.; Ivanov, D.; Larason, W.; Nixon, M.; Moller, H. Accelerated Reported Battery Capacity Loss in 30 kWh Variants of the Nissan Leaf. Preprints 2018, 2018030122 (doi: 10.20944/preprints201803.0122.v1)
Nissan statement via Green Car Reports