I have some firsthand experience with this. I live in Phoenix and had 2011 and 2012 LEAFs. Both lost 15% capacity after 10 months. The 2012 was down about 25% after 2 years. Heat was clearly an issue without a TMS. Today, Nissan released their heat tolerant battery chemistry and announced a cost for a battery replacement: My Nissan Leaf Forum View topic - Update on Nissan LEAF Battery Replacement Anyone think Tesla might release a heat-tolerant battery that might make a TMS unnecessary and perhaps lower the cost? I wonder how heat tolerant Nissan's new battery chemistry actually is.