Seen it before, but it seems they are getting serious
http://carswithcords.blogspot.com/2015/02/tesla-class-range-extender-for-nissan.html?m=1
A total of 85kWh worth of batteries are nestled into the aerodynamic egg-shaped trailer. They claim that, along with your car's original batteries, you can have 300 miles of range.
http://carswithcords.blogspot.com/2015/02/tesla-class-range-extender-for-nissan.html?m=1