Very Interesting what Nissan has achieved with their partner in China. On NHK for the moment. https://www3.nhk.or.jp/nhkworld/en/news/videos/20180512122442940/
This is certainly a better idea than making the customer wait for the charger, but it requires defining a standard for batteries which may prove tricky to implement. I suppose a centrally controlled country like China may be able to force it on manufacturers but I can't see this happening quickly or at all in the west. The other possible problems are that you may get an old battery which carries less charge which might cause problems, and I think the logistics of doing it get pretty horrific if you imagine everyone using this. Problems like where they are to be charged - centrally at a charging depot or at the 'filling' station - need to be solved. Trucking heavy and bulky battery packs around in large quantities doesn't seem a good plan but neither does the idea of charging large numbers of them at every filling station. It is going to take a great deal of space and will require a pretty hefty grid connection for the power required wherever it's done. Also, I wonder what happens if you want to replace a half-empty battery for a full one in anticipation of a long journey between filling stations? Do you get an allowance in return? Who pays if the battery conks out or goes on fire as you are using it? All this needs to be considered too? Further problems arise if there is a change in battery technology. You may well find that a new improved battery requires the car to accept a different voltage. Or the battery may require connection to a heating or cooling system, or the BMS will be designed for one technology and won't be able to handle a different one. A swap to supercapacitors might also happen in which case the car has to accommodate widely changing voltages. On the plus side, however, concerns about range diminish if a battery swap takes only a minute or two, and you don't have to squeeze every last gram of energy density out of the battery design. I seem to recall reading of a battery swap system that was tried in - I think - Israel. I can't remember much about it - I wasn't really very interested - except that it failed and that the chap behind it was a rather high-profile performer with a good line in dramatic presentations - a bit like Musk.