There are three main obstacles to making electric cars a viable alternative to those powered by internal combustion engines: the weight, cost and range of the batteries. Internal combustion engines have range limits based on the size of their fuel tank, but it only takes a few minutes to dump 10-15 gallons of liquid fuel in the tank and be on your way. It takes hours to recharge a battery. Fast charging systems are being developed, but they will require new infrastructure for the high currents and voltages required. The cost issue also works against range. You can reduce cost with a smaller battery, but you know what happens then. A battery with more range is both heavier and more expensive. How about a smaller swappable battery? That's one of the possible alternatives that Tesla is considering for the Model S sedan. This brings a whole different set of problems with it. Even smaller batteries will weigh several hundred pounds, making them difficult to handle. There are also safety issues with handling high voltage batteries. You also need a distribution infrastructure for the batteries and automakers have to standardize on common pack formats to make the whole idea viable. It's not like popping into a drug store for a set of AAs for you camera. Tesla's bright idea just goes to show that electric cars have a long way to go before they can replace internal combustion engines completely.