I guess it depends on how hard it is to swap out a battery but on a vehicle like a bus that can probably be made very simple. Now that I think about it a bus must carry a large quantity of fuel, I wonder how long it takes to fill one up. Swapping a battery could actually be faster.
Depends on battery charging rates but in general, a swap will be faster at large energy densities. BAIC in China are currently experimenting with this in taxis and buses.
