A real-time update on battery capacity loss LEAFS

by Ernie Hernandez on July 31, 2012

It's Electric photo44 LEAFs in three states show battery capacity loss

As reported on the MyNissanLEAF.com (MNL) wiki, there are now a total of 44 LEAFs showing the loss of one or more battery capacity segments. The distribution of these vehicles is in high to very-high temperature parts of the country, which seems to be the overriding commonality to the issue. 34 are in Arizona, 9 are in Texas, with California contributing one as well.

According to Nissan’s letter to LEAF owners of one week ago, this amounts to less than one half of one percent of all LEAFs sold in the United States. According to that open letter, there have been more than 400 LEAFs sold in Arizona. This would mean that over 90 percent of the LEAFs sold in Arizona have not experienced any battery capacity loss – at least that we are aware of. Worth keeping in mind is that not all Arizona LEAF owners likely are present on the MyNissanLEAF forum. Also worth keeping in mind is that the number of LEAF owners reporting a battery capacity loss is growing larger by the week, although in relatively small numbers. As owners report battery capacity loss in various ways (MNL, Facebook, etc), this is certainly not a reliable nor all encompassing  database as it is likely that some instances are, as of yet, unreported.

Here we step into the realm of speculation. The production variance of battery cells may be a contributing factor, especially considering the low overall incidence of occurence. The LEAF battery pack consists of 48 modules made up of four cells each. This total pack size of 192 cells will certainly include some variability of production during the manufacture of these cells. The possibility may exist that only a handful of cells are limiting the storage of the entire pack. It is our understanding that the battery management system (BMS) is designed to protect the battery pack and limiting the maximum capacity with high battery pack temperature may be one way of doing that. Feel free to provide any insight in the comments section to contribute to the discussion.

Nissan has agreed to evaluate several Phoenix area cars to get more hard data regarding this issue. These owners have been provided alternate transportation by Nissan. It is not known how long this evaluation process might take. It seems that Nissan will be looking closely at two factors, and likely more – owner behavior in charging and driving their LEAF and examination of the battery pack at the individual cell level.

We don’t anticipate any rapid results as all of this analysis and examination will take some time. Meantime we will continue reading the overlong thread on MNL to see if we can fill in some of the gaps in our own information.

{ 1 comment… read it below or add one }

indyflick August 1, 2012 at 8:58 am

Given the LEAF battery pack uses passive cooling, I wonder if the issue might be excessive high temperatures of the interior while the car is sitting in the sun. The cars interior is going to get far hotter than the ambient temperature if the windows are up. The body of the car is acting a large heat sink. However, if the heat sink gets hot, then it can actually defeat the system and warm the battery pack.

If I were driving a LEAF in AZ, I would park in the shade and crack all the windows. Or maybe use a car cover in the summer.

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