What Is a Range Extender (REx)?

A range extender (REx) is a small petrol generator fitted inside an electric vehicle that charges the battery while you drive, allowing you to keep moving when the battery alone would run out. It is not the same as a plug-in hybrid: in a REx car, the petrol unit is there purely to generate electricity, not to drive the wheels directly. REx cars were most commonly associated with certain BMW i3 variants. If you are comparing EV types to work out which charging cable you will need, start with the charging cables by car guide.

REx vs full EV vs PHEV: at a glance

How does a range extender actually work?

When the main battery drops below a set threshold, the small petrol generator starts automatically and produces electricity to feed into the motor and partially replenish the battery. The wheels are still driven electrically at all times: the petrol never connects to the drivetrain mechanically. This keeps the driving feel consistent regardless of whether the generator is running. The downside is that a small generator produces a limited amount of power, which can be inadequate when you are already demanding high output, such as during fast motorway overtaking or long uphill stretches.

Does a REx vehicle still need to be plugged in?

Yes. A REx car is still fundamentally an electric vehicle and benefits from regular charging at home or at public points. The petrol generator is a backup for longer journeys, not a substitute for charging. Driving on the generator alone for extended periods is inefficient and can place strain on the system. Most manufacturers specify a recommended minimum battery state before the generator kicks in, and some limit how long the generator can run continuously. Treating it as a true EV with a backup safety net is the right framing.

What are the practical drawbacks of a REx?

The petrol generator adds weight to the car, which reduces the overall efficiency of the electric drivetrain. It also introduces an additional combustion component that requires servicing, including oil changes and spark plug maintenance. Boot space is sometimes reduced to accommodate the generator and its small fuel tank. On sustained motorway journeys at high speed, the generator may not keep pace with energy demand, so the battery can still deplete if you drive hard for long enough. Finally, because you are still burning petrol, a REx car cannot match the zero-emission credentials of a full battery EV.

Are range extender EVs still being made?

Very few manufacturers produce new REx models today. As battery technology has improved, full EVs can now cover distances that once required a backup generator, making the REx format less compelling for most buyers. The BMW i3 REx was the most widely known example in the UK market, but production ended. Some newer extended-range electric vehicles (EREVs) from certain manufacturers do use a similar principle, though they are not widely sold in the UK market yet. The general trend is toward larger batteries, faster charging networks, and full EVs rather than hybrid solutions.

How does charging a REx car compare to a standard EV?

The charging process is identical to any other battery electric vehicle. You plug in at home using a wallbox or a three-pin socket, or use public charging points, and the battery charges as normal. A Type 2 charging cable is the standard for home wallboxes and most public AC chargers in the UK. Because the battery in a REx model is typically smaller than that of a comparable full EV, it may charge to full more quickly, though this varies by model. If you travel to places without charging infrastructure, a portable EV charger gives you flexibility to top up from a standard socket.

Frequently asked questions

Is a range extender the same as a hybrid?

No. In a REx car, the petrol engine never drives the wheels directly; it only generates electricity. In a standard hybrid or PHEV, the combustion engine can drive the wheels mechanically at higher speeds. The distinction matters for emissions classification, tax treatment, and how the car feels to drive at motorway speeds.

Do I need a special charger for a REx EV?

No. A REx car uses exactly the same charging infrastructure as any other battery EV. A Type 2 cable and a home wallbox cover the vast majority of charging needs. At public rapid chargers, the connector type depends on your specific model, so check the car's manual or the reg checker on the home page before you travel.

Will the petrol generator start automatically?

Yes, on most REx vehicles the generator starts automatically when the battery drops to a pre-set level. Some models allow you to hold a battery reserve manually, which is useful if you know you will need the generator later in a journey. The car's display will indicate when the generator is running.

Can I drive a REx car past 2030 in the UK?

The UK government currently plans to end the sale of new petrol and diesel cars in 2030. Existing REx vehicles already on the road will not be banned from use. Whether future regulations affect how REx cars are taxed or permitted in clean air zones is subject to ongoing policy changes, so check gov.uk for the latest guidance.

Is a REx car cheaper to run than a PHEV?

On short daily journeys driven entirely on electricity, running costs are similar to a full EV for both types. On longer journeys where the petrol backup is used, costs depend on current fuel prices and how much of the trip relies on the generator. Check current petrol and electricity rates to model your specific usage rather than relying on any fixed figure.

Should I buy a REx EV or a full EV in 2024?

For most buyers, a full battery EV with a decent range and access to a home charger is now the more practical and lower-maintenance choice. A REx car may suit someone who occasionally makes long journeys but cannot always guarantee access to a rapid charger, though the limited availability of new REx models makes this a difficult choice to act on today.

If you are weighing up different EV types and want to understand what charging equipment you will need, the charging cables by car page covers every major model sold in the UK. For more detail on connectors, speeds, and what works where, browse the full EV guides library.