Some electric vehicles claim to be able to travel over 1,300km before needing to be plugged in to be recharged. What is the secret?

All hybrid electric vehicles (HEVs) have internal combustion engines (ICE) as their primary driving unit. Drive to the wheels can come from the electric motor, the engine or both at the same time. When operating together, the motor provides a useful torque boost to the ICE, particularly during mid-range acceleration or when moving off from rest.

Of more interest to the motorist is the fact that the hybrid powertrain can reduce petrol consumption because the engine does not have to work as hard.

The hybrid’s battery can be charged by regeneration during coasting or braking. It can also be charged directly by the engine when the battery level drops to a minimum state of charge.

Plug-in hybrid electric vehicles (PHEVs) offer another way. These have a charging port, allowing the battery to be charged using an EV charger. If a charging station is available at home or at work, you can charge the battery and maximise pure-electric operation, drastically reducing fuel consumption.

The latest adaptations of electrically driven vehicles are known as extended-range electric vehicles (EREVs). Like PHEVs, these vehicles can be plugged in to charge the battery and there is an ICE.

That is where the similarity ends.

An EREV’s drive is provided solely by the electric motor, which is powered by batteries. Current-generation EREVs typically offer up to 200km of electric-motor driving before the battery is depleted. Thereafter, the EREV needs to be plugged in.

Alternatively – and here is the main difference from the PHEV – the ICE is automatically activated to charge the battery. The petrol-fuelled engine, which tends to be quite small, is essentially a generator which runs only to charge the battery. As such, there is no need for the rather complex transmission to couple the engine to the motor and driving wheels that is necessary in a PHEV.

Since the engine does no wo...