Range anxiety may keep you from driving an electric car right now, but Tesla chief Elon Musk doesn't expect that to be a problem for very long. When grilled about driving distances in a Danish interview, Musk revealed that he expects the battery technology to improve at a rate of 5 to 10 percent per year, which could lead to some massive range gains in a relatively short space of time. The CEO notes that people have already driven the Model S up to 500 miles on a charge at slow speeds, and that this could extend to over 600 miles as soon as 2016, and a whopping 746 miles by 2020. While it's doubtful that you'd get these figures blazing down the highway, Treehugger's back-of-the-napkin math suggests that this should still lead to a realistic range of 382 to 483 miles. That's enough for many city-to-city trips, and it doesn't account for lighter materials or other efficiency refinements.