swappable battery is important for those who need to drive beyond the battery range or don't have a good option to easily charge their cars overnight. This could be for people who live in big cities like San Francisco (although you can imaging a plug every parking spot 20 years from now) or for people who maybe going on a road trip. Which would make you wonder if people would not have two cars. One for daily commute the other for extended activity that might be fueled by some form of biodiesel. Hydrogen might also be another good solution at some point. This is something I proposed a long ago as part of my high school science fair. Basically using electricity for electrolysis of water to get hydrogen. You can the use the hydrogen as fuel cell or in combustion form for these long-range road trips instead of swapping batteries.