Doesn’t seem like having two (or more) battery sets to swap out is a particularly economical means of providing motive power. Those battery packs can’t be cheap, by any means, and the machinery to carry out the swap has to be of almost industrial-grade fork lift variety.
Plus the charging station....
It still makes more sense to have an on-board hydrogen fuel cell for the generation of electricity to provide motive power.
current Tesla batteries for the 60k S class model go about 280 miles per charge http://www.teslamotors.com/goelectric#range