It's pretty clear that Nissan will need to do something to handle hot climates better. LEAFs in hot climates like Phoenix are losing capacity very quickly. On the other hand, LEAFs in cool climates like Seattle appear to be doing very well even when driven a LOT (there's a
guy near Seattle who put nearly 40k miles in a year, 130 miles/day, 2 full charges/day, with very little capacity loss).
There's two situations where some sort of active cooling can really benefit the LEAF:
1. Quick charges when the battery is warm - quick charging seems to generate a good amount of heat in the battery pack. In moderate temps with occasional use, it's not an issue. But if you QC more than once a day or the pack is already warm (from high ambient temps), the battery pack temp can get pretty high. It takes quite a few to get the battery up to the red zone on the battery temp gauge, but the hotter the battery is, the faster it's degrading.
2. High ambient temps - there's a huge difference in rate of capacity loss comparing Phoenix to Seattle, for example. In Phoenix and similar climates, it seems to be a given that you will lose 15% capacity in about a year - seems to vary between 10-20%. Seattle LEAFs are seeing less than 5% capacity loss after a year, even with lots of miles. Some sort of TMS to help keep battery temps under 90F if not lower at least would go a long ways maintaining capacity in hot climates. Even if the TMS only ran when plugged in at night it would be a huge benefit. For half the year in Phoenix the typical LEAF won't see it's pack go under 90F - especially if parked in a garage which doesn't cool much during the night. You could probably reduce rate of capacity loss by a large amount especially considering that the battery pack is a large thermal mass and takes time to heat up under normal conditions.
Of course - there's another alternative to TMS. Since battery degradation seems to flatten out around 30% capacity loss (at least that's what Nissan says, Tesla has said similar things about their battery), it might be easier to simply bump up new capacity by 30% and be absolutely up front with the type of capacity loss one will see and how it varies with climate using various cities as examples. If you properly manage customer's expectations, then capacity loss isn't an issue. The biggest issue with capacity loss in hot climates today is that Nissan has only given a blanket 20% after 5 years and 30% after 10 years with no mention that if you life in Arizona you're actually going to see 20% lost after 1-2 years and 30% after 2-4 years.
70 mile range is already borderline for many people - even 20% cuts that down to 56 miles - and losing those 14 miles after 1 year instead of gradually over 5 years represents a large loss in value to the customer.
Surely, Nissan knew this would happen ahead of time - many were surprised to see Phoenix as a launch market and took it as a vote of confidence in battery durability in hot climates and have been left sorely disappointed. If Nissan doesn't do something soon to get this under control, it's quickly going to snowball into a PR nightmare. Anecdotal stories on mynissanleaf.com has shown that a good number of customers are no longer looking at the LEAF until this capacity degradation issue is resolved. A handful have sold/traded in their LEAF after a year because of it - some have traded it in for a new lease on a LEAF - some have gone back to a hybrid.
If they start having to replace a bunch of batteries under warranty, I'm sure they'll make some changes.
While loss of capacity has been rapid in hot climates, there have been very few reports of actual battery pack failures. I certainly can't recall any - the cells that Nissan is using appear to be very consistent in performance.
There is apparently a small fan in the pack to at least circulate air around to distribute heat evenly and perhaps aid some passive heat radiation away from the pack.
I've neard this rumor multiple times, but the service manual doesn't appear to mention it...
