I have been thinking about battery trailers for a long time as perhaps a better solution than expensive battery swap stations or scattered supercharging locations.
Why? Because we all know that 90+% of most people's daily driving can be done without any of these things, and as batteries get better this infrastructure will be used less and less until becoming obsolete (not a very good business model).
I have thought Tesla could produce their own battery trailer to take the Model S range up to 500 miles.
500 miles seems to be the holy grail for me in terms of range anxiety, as most people cannot drive for more than 500 miles in one sitting and will need to rest/sleep after that much driving, providing an opportunity to recharge overnight.