Range extender

A range extender is a fuel-based auxiliary power unit (APU) fitted to an electric vehicle that drives an electric generator to recharge the traction battery when it is depleted, thereby extending the vehicle's range beyond what the battery alone provides. This series configuration is known as a series hybrid drivetrain, in which the combustion source generates electricity rather than driving the wheels directly. The most commonly used range extenders are internal combustion engines, but fuel cells, microturbines, free-piston engines, and other generator types have also been developed.

Vehicles fitted with a range extender are referred to as extended-range electric vehicles (REEVs or EREVs).