What is a mild hybrid vehicle?

You may have heard the car referred to as a "mild hybrid", but what does that really mean? How is it different from other types of hybrid vehicles? And does it need to be connected? Read on to find out.

What is a mild hybrid?

A mild hybrid vehicle (also known as a mild hybrid electric vehicle or MHEV) has a gasoline or diesel combustion engine and a small battery-powered electric motor that helps improve fuel economy while reducing carbon emissions.

Mild hybrids are the simplest form of a hybrid vehicle. They differ from conventional hybrids (often referred to as full hybrids or "self-charging" hybrids) and plug-in hybrids because the electric motor does not drive the wheels directly. Instead, the mild hybrid's job is to help the engine, especially when accelerating. It can improve your vehicle's fuel economy and reduce exhaust emissions compared to a conventional gasoline or diesel vehicle.

Mild hybrid systems work slightly differently for different car manufacturers, but they all follow this general principle. Since mild hybrid vehicles are simpler than other hybrid systems, they are usually more affordable to purchase.

Fiat 500

How does a mild hybrid work?

The electric motor in a mild hybrid vehicle is a battery-powered "starter-alternator" that replaces the starter and alternator you'd normally find in gasoline or diesel vehicles.

The alternator starts the engine and powers most of the vehicle's electrical equipment. It also stores the energy generated by braking and, in most mild hybrids, uses this energy to help the engine accelerate. This means the engine has less work to do, which means it consumes less fuel.

Volvo XC40

What is the difference between a mild hybrid and a regular hybrid?

All hybrid vehicles use battery-powered electrical systems to provide better fuel economy than if they had engines alone. A conventional full hybrid has an electric motor connected directly to the wheel, which in most cases means the car can only run on electricity for short distances without exhaust emissions.

But the mild hybrid's electrical system isn't connected to the wheels, so you can't run it purely on electric power. Read more about the differences between mild hybrids, self-charging hybrids and plug-in hybrids here.

Land Rover Discovery Sport

How are mild hybrid batteries charged?

The batteries that power mild hybrid systems are charged by "regenerative" braking. This means that when you step on the brake pedal, or even just release the gas pedal, the starter-alternator reverses its rotation and generates electricity that goes back to the batteries.

You don't plug the mild hybrid into a power outlet to charge its batteries. Only plug-in hybrids and electric vehicles are charged this way.

Ford Puma

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What is it like to drive a mild hybrid?

Driving a mild hybrid is similar to driving a "regular" car, but there are slight differences. Most modern cars have a stop/start system that shuts off the engine when you stop to save fuel. But in a mild hybrid, this function is taken care of by its starter/alternator, which usually means you experience less jolt when starting the engine - you may not even notice it.

Regenerative braking that recharges the battery can affect the sensitivity of the brakes and the vehicle may slow down more than you expect when you apply the brakes or release the accelerator pedal. It may seem a little strange at first, but you will soon get used to it.

Some mild hybrid systems are powerful enough to increase engine acceleration, but you will probably only notice the difference if you drive a mild hybrid vehicle immediately after driving a conventional model.

Fiat 500

How economical are mild hybrid cars?

There is no hard and fast rule for fuel economy that you can expect from a mild hybrid car, but it should be better than a car with a conventional gasoline or diesel engine. 

Otherwise, the usual principles apply. A large heavy car with a powerful engine consumes more fuel than a small light car with less power, whether or not it is a mild hybrid.

Are there any disadvantages to mild hybrids?

Although mild hybrid systems reduce your vehicle's fuel consumption and carbon emissions, the reduction is not as great as with a conventional hybrid or plug-in hybrid. Mild-hybrid cars also don't give you the option to use only the zero-emissions electricity you get with all plug-in hybrids and most full hybrids. 

Some mild-hybrid models cost a bit more than the same non-mild-hybrid version, but the technology is quickly becoming the norm for newer vehicles.

Ford Fiesta

What are the benefits of mild hybrids?

In most cases, mild hybrids give you better fuel economy and emit less carbon dioxide, which should reduce the amount of vehicle excise duty (car tax) you'll have to pay. The engine generally feels smoother and more responsive, making driving easier and more enjoyable.

Which car brands produce mild hybrids?

Most automotive brands already have several mild-hybrid models in their range. For example, every new non-plug-in hybrid version of the latest BMW 5 Series is a mild hybrid, while almost all new Volvo cars are either mild hybrids, plug-in hybrids or all-electric vehicles. Every new Fiat 500 is also a mild hybrid, although Fiat labels the car simply as a "hybrid".

Over the next few years, almost every car that is not self-charging, plug-in hybrid or all-electric will need to be a mild hybrid in order to meet the latest emission standards.

Volvo S60

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