I'm fairly sure there is no active cooling in the Leaf battery pack. I asked that question directly of Mark Perry, and when I've seen the display pack, there is no fan that I have seen. I have never heard a fan running while the Leaf pack is charging; like there is on my brother's i MiEV, for example.
The
Wikipedia entry on the Leaf battery does not mention anything about cooling.
Here it specifically discusses the fact that it has no cooling system.
They do say you need to avoid having the car in 120F+ heat for more than 24 hours. And maybe they will need a revision for hot climates?