Three electric taxis with replaceable batteries began service recently in Tokyo. They are participating in a 90 day trial to test the practical issues arising from real world service in a huge city. The taxis are available on the first floor of the Roppongi Hills center.
Three vehicles is certainly not a large number in a city with 60,000 taxis and 13 million people. However, the rollout is being tested and managed very carefully due to the newness of the technology. Battery swapping for electric vehicles is actually quite different from conventional fuel options. For one thing, the batteries reportedly can be changed in 60 seconds. To see a battery change and battery storage facility watch this video:
The Tokyo test is meant to demonstrate that taxis in cities all over the world could use this technology to reduce local air pollution. New York City has over 50,000 for-hire vehicles. Hong Kong has over 18,000 taxis. Even if half of these vehicles in the future are replaced with, or converted to electric, air pollution could be reduced significantly.
Better Place is the company responsible for the battery-switching technology and taxi conversion from gasoline to electricity. They plan to launch electric vehicle battery switching and charging networks in Israel, Denmark and Hawaii in the near future.