What is a mild hybrid car and should you buy one?

Hybrid cars – combining an engine and an electric motor to improve fuel economy and reduce emissions – have been a familiar concept since the launch of the Toyota Prius.

In recent years, we've seen the arrival of plug-in hybrids (PHEVs), which can be plugged in and charged up. And another variation on the theme is the mild hybrid (MHEV).

Many car makers now offer models fitted with MHEV (or mHEV) technology. But what is an MHEV, how does it work and should you buy one? Read on to find out more...

What is a mild-hybrid car?

MHEVs are more common than you might expect, because mild-hybrid tech is relatively inexpensive to fit, and reduces the fuel consumption and CO2 emissions of both petrol and diesel-engined cars.

It might not be immediately obvious from a model's name that it's an MHEV. For example, the mild-hybrid VW Golf is badged the eTSI, while the Fiat 500 Hybrid and Suzuki Swift Hybrid are MHEVs rather than regular hybrids.

Generally, a mild hybrid has a small electric generator instead of a traditional starter motor and alternator (the device that keeps the 12-volt battery charged), plus a lithium-ion battery.

Most mild hybrids run on a 48-volt electrical system – a higher voltage than the electrical systems of traditional combustion engines use. The 48V system powers components that would have previously been powered by the engine, enabling it to operate more efficiently.

How do mild-hybrid cars work?

As the name suggests, a mild-hybrid car provides only gentle electrical assistance to the engine. While regular hybrids (also known as full hybrids) and plug-in hybrids can be driven on electric power alone, an MHEV cannot.

Mild-hybrid systems work in slightly different ways depending on which car manufacturer has developed them. In general they assist the engine under hard acceleration and help make the car's stop-start system operate more smoothly.

MHEVs also use regenerative braking to harvest energy when the brakes are applied or when the car is coasting. That energy is converted into electricity that's fed into a lithium-ion battery and stored until it's needed to provide extra assistance. On average, a car with mild-hybrid technology can be around 15% more efficient than its conventional counterpart.

Read more: The best full hybrid and plug-in hybrid cars

One prime example of mild-hybrid tech being used to enhance the economy and performance of a car is the Ford Puma.

Most versions of the model come with Ford’s 1.0-litre three-cylinder mild-hybrid petrol engine, which is also used in versions of the Ford Focus and Ford Kuga. Ford says the system continuously monitors how the car is being driven to determine how intensively to charge the battery and when to assist the engine.

The system on the Puma can give the engine an extra 15lb ft of pulling power, so it doesn’t have to work as hard under normal loads, and can deliver a 10% improvement in fuel economy. The same boost can be applied when the engine is under heavy load to improve performance, delivering up to 20% faster acceleration.

Are all mild-hybrid systems the same?

No. There's a wide range of mild-hybrid systems, and some are more sophisticated than others. One of the cleverest is in the Audi Q8 luxury SUV.

It goes to even greater lengths to improve economy by working with the car’s adaptive cruise control system to slow it down as it approaches corners and roundabouts, reaping the energy from the regenerative braking. It can even deactivate the engine and let the car coast for up to 40 seconds at a time to save fuel.

Are mild hybrids the same as hybrids?

Mild hybrids are the same as other hybrids in the sense that they use a combination of a petrol or diesel engine alongside some electrical assistance. But unlike full hybrids, they’re not able to run on electric power alone because the assistance the motor provides is, as their name suggests, mild.

Do mild hybrids need charging?

No – in fact, you can’t plug in a mild-hybrid car. Because the batteries are small, electricity is generated as you drive along, rather than relying on a mains power supply as you would with a plug-in hybrid. Indeed, for those without easy access to a home EV charger who are looking to minimise their fuel bills, a mild hybrid could be a sound choice.

Read more: The best hybrid cars you don't have to plug in

Are mild hybrid cars cheaper to tax?

Mild hybrids aren’t as economical as many full hybrid cars and PHEVs, and they don’t benefit from the lowest rates of company car tax.

However, for private buyers, the mild-hybrid road tax rate is a little cheaper than for a pure petrol or diesel, because most are termed as "alternative fuel", so they get the same £10 annual discount enjoyed by owners of full and plug-in hybrid cars in the 2023-24 tax year.

Why should you consider a mild-hybrid car?

For a start, they’re less complex than other hybrids, so in many cases they’re cheaper to buy. They’re also easier to live with than PHEVs, which need to be plugged in regularly to get the best efficiency.

If a PHEV is too expensive or you don’t have access to a charger, a mild hybrid is a cleaner option than a conventional petrol or diesel. They’re also no different to drive than conventional models and work with cars with manual gearboxes, so they’re a good option for those who want to stick with a more traditional driving experience.

Still not sure whether to buy a mild hybrid? These pros and cons should help you decide:

The benefits of driving a mild-hybrid car

– No different to drive than a regular petrol or diesel-powered car
– They don’t need to be plugged in to save fuel, as is the case with plug-in hybrid models
– They’re generally cheaper to buy than a full hybrid or plug-in hybrid car
– Fuel economy and CO2 emissions are improved, reducing bill bills and VED tax
– The technology works with manual and automatic, and petrol and diesel models

The drawbacks of mild hybrids

– They can’t run on electricity alone
– They produce more tailpipe emissions than other kinds of hybrids
– Full and plug-in hybrids are more economical

What cars are available as mild hybrids (MHEVs)?

Many of the most popular cars on sale are available with mild-hybrid technology. In many cases "mild hybrid" or "MHEV" does not feature on any badging to advertise the tech is fitted, so they often fly under the radar.

Models available with mild-hybrid technology in the UK include:

Audi A3
BMW 1 Series
Dacia Jogger
Fiat 500 Hybrid
Ford Puma 
Jaguar E-Pace
Jaguar F-Pace
Kia Sportage
Land Rover Defender
Mercedes A-Class
Nissan Qashqai
Range Rover Sport
Suzuki Swift Hybrid
VW Golf
Volvo XC40

(Click on the links to be taken to our new car reviews of each model.)

What are the other types of hybrids? 

All hybrids have a conventional engine, an electric motor and a battery, although the size and capacity of these varies. As well as mild hybrids, there are three other types of hybrids, and each works in a different way. They are:

Parallel hybrids 

This is where the hybrid story started, and the (now off-sale) Toyota Prius is the most widely known example of a parallel hybrid.

The car’s wheels can be powered directly by the engine, by the electric motor alone, or by both power sources working together. When pulling away and at speeds of up to 15mph, it uses only the electric motor for power, making it very frugal in city driving. The petrol engine cuts in as speed increases and under hard acceleration.

Whenever you decelerate or use the brakes, the regenerative braking system harvests electricity and stores it in the battery for use later on, but the car can run solely on electricity for only up to 1.25 miles. The system is also used in the Toyota Yaris and Toyota Corolla hatchbacks. Models from premium sister brand Lexus work on the same basis.

Range-extender hybrids

Range-extender hybrids – also known as serial hybrids – differ from regular hybrids in that their combustion engines are there mainly to act as generators, producing electricity to power the electric motors, which drive the wheels. 

The latest Honda Jazz is one popular example. It uses two electric motors, powered by a compact battery, working alongside a frugal 1.5-litre petrol engine. The wheels are almost exclusively driven by the electric motors, and the only time the wheels are actually driven by the engine is at higher speeds when it is directly connected to the wheels.

The Honda CR-V e:HEV, the Honda Civic, the Mazda MX-30 R-EV plus the E-Power versions of the Nissan Qashqai are range-extender hybrids too. According to Nissan, the range-extender system gives the Qashqai better performance than you’d get from an equivalent parallel hybrid.

Plug-in hybrids (PHEVs)

These are a halfway house between regular hybrids and full electric cars, and are being offered by a growing number of brands. As the name implies, they can be plugged into an electrical outlet to recharge their batteries. 

Although PHEVs have conventional engines, they also have larger batteries than regular hybrids and can go further on electric power alone, greatly reducing running costs if they’re charged regularly.

One of our favourite PHEVs is the Lexus NX 450h, which has an official electric range of 43 miles – 13 miles longer than the BMW X3 xDrive30e. According to our testers, if you can plug the NX in regularly and mostly do short journeys, you could achieve as much as 313mpg. When the batteries have run out, it still has fuel economy of close to 40mpg.

Read more: The best plug-in hybrid cars

Read more: The most fuel-efficient cars in the UK

Read more: Every brand's cheapest new car

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