Teslas have active battery temperature management, even when parked in "deep sleep" mode, and very robust heating and cooling capacity. Left on a hot Arizona parking lot, our Model S will occasionally run the AC for the battery. This is a huge improvement over our Leaf, which lost 30% of its battery capacity during a single summer of being parked on Scottsdale blacktop.
So given all this, how long do the original batteries last in California heart?