Yes, that's approximately correct. The shortest-range S gets 160mi per charge. 500 * 160 = 80,000 miles, which isn't bad for the first scheduled maintenance. In fact, Tesla guarantees their batteries to 100,000 miles. If the battery costs $20K to replace, well, a gas engine + transmission + exhaust system in a $60,000 car depreciates as much in that time, too.