Keep in mind the battery temp gauge has huge overlapping ranges: http://www.electricvehiclewiki.com/Battery#Battery_Temperature_Gauge.
I'm not sure how useful the graph Isaac cited it as it this point. I believe it was created during the crap '11 and '12 batteries (during the Phoenix capacity loss fiasco) and doesn't reflect the 4/2013+ '13 and '14 Leaf batteries, the "lizard" batteries on the '15 nor the '16 and '17 30 kWh batteries, to name a few.
It seems the 4/2013+ batteries hold up better. The lizard batteries are even better while the signs for the 30 kWh batteries have been surprisingly bad. Not clear if the alarming 30 kWh capacity bar losses are due to some folks having defective packs or cells or some characteristic of a (production) run between a certain time span or a.... quirk those packs, in general.
Nissan has never been forthcoming w/publicly releasing any sort of data on degradation (e.g. time vs. temperature for a given chemistry) for any of its batteries and when there have been tweaks to the chemistry. Best we got were references to a "hot" battery that was in testing aka "lizard" battery. Only notification we got about its release was http://www.mynissanleaf.com/viewtopic.php?f=4&t=17168. Notice the lack of details?
BTW, https://www.youtube.com/watch?v=Vz2WzLQ2tqg (from a MNLer) shows 0 temp bars. I wish I could chill my batteries down to that low. I think my pack would last pretty long if I could do that each night.