At the end of November 2016 I took my LEAF in to get the traction battery replaced as it had worn out. I have been tracking the status of the new battery using an application called LEAF Spy Pro. This app uses the OBDII diagnostics port to read data every 5 seconds on hundreds of parameters and logs them into my dropbox folder each day as I arrive home.
At six months I decided to look to see if the new battery is holding up or wearing out. The outcome looks favorable, compared to the capacity of the new battery it has lost 1.4% of total capacity. It’s dangerous to extrapolate forward so early but just for fun this would mean the battery has a 10 year life. Much better than the original which lasted just 5 years.
The new battery has exhibited interesting swings in capacity over the last 6 months. On January 23rd this year the capacity was down 4.5%. Indicating a projected life worse than the original battery. I was concerned I had bought a dud. However by mid March the battery was back to full capacity showing no loss whatsoever.
Another interesting observation is that the capacity has never exceeded 66.141 Ahr, it seems to return to this value occasionally and seems to “stick” at this value for a week or two.
Another battery parameter named Hx, the meaning of which is uncertain, is thought to reflect overall battery health. It doesn’t appear to have a maximum value, it moves up and down freely. This parameter has varied by over 7% in the last six months.
The battery appears to lose some capacity and somehow regain all the lost capacity, then lose it again and regain again. This is very odd behaviour for a rechargeable battery, one expects a short term initial gain as the battery matures then a continual gradual capacity loss; certainly little to no gains after the battery has reached its maximum capacity.
This behaviour has been observed by other LEAF enthusiasts who have monitored their new batteries closely as I have. What is going on isn’t clear, the most credible theory is that Nissan have added some “Hidden Capacity” that the battery management system keeps in reserve without reporting its presence and occasionally taps into this reserve when capacity is permanently lost. It’s just a theory, but it does match the data. LEAF enthusiasts that have had the new battery for more than a year report that the battery eventually stops regaining capacity and then loses capacity at a more consistent and predictable rate. This suggests this regaining of capacity will be short lived.
I’ll report the batteries status again at one year, which will be the end of November.