Nissan Press Release
Nissan Technical Presentation - YouTube
For electric drivetrain, there is a continuum for single "charge" range, battery size and charging flexibility (grid vs gas).
BMW explored this with the ReX i3 -- you have a battery that can be charged while driving with the small gas engine.
Nissan is pushing this boundary more with e-Power. Nissan's effort allows you to carry a much smaller battery with a highly efficient gas engine charging the battery on the go. In their presentation, Nissan mentions 1/50-th the battery size for e-Power compared to pure-EV -- that sounds much too small. Maybe, they meant 1/5-th -- there was a translation mistake.
All auto makers are betting on their projection of how the transition to EV will occur over the next 5, 10, 20, 30+ years.
It will be interesting to see it play out -- I bet that a high-efficiency gas engine for powering a battery-driven EV drivetrain will take more than 50% of the US market for at least 10+ years before we get to 50% market share for pure-EVs.
Follow-up: I think decoupling the gas engine from the drivetrain is the main improvement to be had -- once you do this, you can optimize the gas engine for electrical power generation independent of vehicle speed.