What is a range extender?

Range extenders are another form of electric cars. They help eliminate range anxiety while maintaining many of the benefits of an all-electric car

You will likely have come across the terms electric car, hybrid and plug-in hybrid, and even a hydrogen car, but the term range extender may be less known.

They’re a type of electric vehicle that combines both an electric drivetrain, complete with a battery and electric motors, as well as an internal combustion engine. However, the crucial difference between a range extender and a plug-in hybrid is that the internal combustion engine never drives the vehicle.

How a range extender works

An easy way to understand what a range extender is, is to think of it as an electric car that also comes with an engine used to recharge the batteries on board. Unlike a plug-in hybrid where the engine is used to drive the car, in a range extender the engine (most often a petrol unit) is used to only recharge the batteries while on the move.

The difference is small, but important. This means that a range extender will always be driven by the electric motor and drivetrain, meaning it always drives the same. A plug-in hybrid switches between electric and engine power meaning its driving characteristics change depending on which unit is powering the wheels.

A range extender has to be both recharged and refuelled. The batteries are charged like any other electric vehicle, while the engine is topped up with fuel at forecourts.

Range extenders have been a niche choice, and the only model you can currently buy new is the BMW i8 supercar.

The BMW i3 was, until recently, available as a fully-electric model and as a range extender. The pure electric model has an estimated range of 125 miles.

However the i3 REX, as it was often known, featured a two-cylinder 0.9-litre petrol engine, adding up to 93 miles of electric range when in use. The engine would turn on when needed after the battery charge dips below a certain point.

Pros and cons of a range extender

The big selling point behind a range extender is that it effectively erases range anxiety. This is because the petrol unit not only adds a significant boost to the vehicle’s range, but also because this means it can be topped up at regular fuel stations without the need to plug the vehicle in for charge.

However, a downside to range extenders is that they are not tax exempt under the current Vehicle Excise Duty rates. This is because with the engine on board, they emit tailpipe emissions. The BMW i8 emits 49g/km CO2 – meaning that it’s free for the first year, but subsequent years cost £130.