PHEVs vs REVs
Range extender vehicles (REV), also referred to as extended range electric vehicles (EREV), are effectively battery electric vehicles (BEVs) with a small internal combustion engine that is used to generate additional electricity.
REVs are typically considered as either BEVs (by the previous definition) or plug-in hybrid electric vehicles (PHEVs) due to the inclusion of an engine. What separates the engines in REVs from PHEVs, however, is that their purpose is to supply the traction battery and electric motor with power rather than propel the vehicle. When the battery in a REV reaches a certain level, the engine is turned on to power a generator that recharges the battery as you drive, thus powering the electric motor.