Range extender

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

Types of range extender

Internal combustion engine

The great majority of deployed range extenders use a reciprocating internal combustion engine driving a generator. Because the engine in a series-hybrid configuration does not need to vary its output in line with vehicle speed or load, as that task is handled by the electric motor and battery, the engine can be sized to the vehicle's average power requirement rather than its peak demand, and can operate at or near its most thermally efficient rotational speed. This reduces fuel consumption during range-extension operation and, compared to a conventional drivetrain engine subjected to varying loads, reduces wear.

Engine displacements in automotive range extenders have typically been 0.6–1.5 litres for passenger vehicles. Mazda used a compact Wankel engine of 830 cc in the MX-30 R-EV, taking advantage of the rotary engine's compactness relative to its power output. Heavy-duty applications such as pickup trucks have used larger engines. For example, the Ram 1500 REV uses a 3.6-litre V6 petrol engine as its generator.

Wankel and rotary engines

The Wankel engine has attracted interest as a range extender because of its high power-to-weight ratio and compact dimensions relative to displacement. It operates most efficiently at constant speed, making the generator-only application in an extended-range electric vehicle a better fit than in a conventional drivetrain where varying speed demands reduce rotary engine efficiency. Mazda deployed a production Wankel range extender in the MX-30 R-EV and has conducted research into hydrogen-fuelled rotary range extenders.

Free-piston linear generator

A free-piston linear generator (FPLG) replaces the conventional crankshaft-and-rod mechanism with a piston that oscillates freely between combustion and rebound chambers, driving a linear alternator directly. The absence of the crankshaft eliminates friction losses associated with converting linear to rotary motion, and the device can accept a wider range of fuels including hydrogen and biofuels. Free-piston designs have demonstrated higher efficiencies and lower noise, vibration, and harshness than equivalent crankshaft engines in laboratory conditions, though as of 2025 no free-piston range extender had entered production.

Microturbine

Microturbines offer a high power-to-weight ratio and the ability to run on multiple fuels, including natural gas, biogas, and hydrogen, while producing low emissions. A 35 kW microturbine range extender has been estimated to be approximately 50% lighter and 40% smaller than an equivalent piston engine, with thermal efficiency of 30–35%. Turbines operate most efficiently at steady, constant speed, making the generator-only role in a range-extended vehicle a better match than variable-speed automotive applications. Engineering organisations including Delta Motorsport (with Cosworth) and Wrightspeed have developed automotive microturbine range extenders; no microturbine-based range extender had entered volume passenger-vehicle production as of 2025, though the technology has been demonstrated in commercial truck applications.

Fuel cell

A fuel cell converts hydrogen or other fuel directly to electricity through an electrochemical reaction, without combustion. Fuel cells are more efficient than combustion engines in steady-state generation and produce no local emissions when using hydrogen. Hydrogen fuel cells have been used as range extenders in battery electric buses — for example, the Mercedes-Benz eCitaro fuel-cell variant achieves a range of approximately 400 km (250 mi) compared to 280 km (170 mi) for the battery-only version, using a 60 kW Toyota fuel cell to recharge the battery. Practical barriers to fuel-cell range extenders in passenger vehicles include limited hydrogen refuelling infrastructure, the cost of fuel cell stacks, and the challenges of on-board hydrogen storage.