The term Mild-Hybrid is commonplace nowadays, with most manufacturers making them in some form, but what exactly is a mild hybrid?

In this article, we’ll cover exactly what they are, how they work and whether you should consider one for your next car.

What is a Mild Hybrid?

A mild hybrid is a car that features a small electric motor alongside a petrol or diesel engine, but unlike full hybrids, it doesn't have the ability to drive solely on electric power. Both the motor and battery are much smaller than other hybrid vehicles.

The electric motor helps assist the engine during acceleration, and recovers energy during braking, helping to boost fuel efficiency and lower emissions. Mild Hybrids, unlike plug in or full hybrids, are usually only slightly more expensive than the petrol or diesel equivalent, thanks to their simplicity.

How Does a Mild Hybrid Work?

In a mild hybrid car, the electric motor works in tandem with the internal combustion engine (ICE). It doesn't drive the wheels by itself but contributes power to the engine in certain situations, such as when you accelerate from a standstill.

One key difference between mild hybrids and full or plug-in hybrids is that the electric motor is not connected directly to the drivetrain, it is instead connected to the engine. In many cases, the MHEV motor replaces the traditional starter motor, this means that the car can retain a traditional clutch and gearbox.

Can a Mild Hybrid Run on Electricity Only?

No, a mild hybrid cannot run purely on electricity, unlike full hybrid or plug-in hybrids (PHEV), which can travel short distances on electric power. Mild hybrids are powered by their petrol and diesel engines 100% of the time, with short periods of assistance from the motor.

Do Mild Hybrids Charge While Driving?

Yes! Mild hybrids do indeed charge their small battery while driving, this is the only way the battery can be charged. As you decelerate, the electric motor acts as a generator and feeds some of that energy back into the battery - this is known as regenerative braking.

Can You Charge a Mild Hybrid?

No, you cannot plug in a mild hybrid to charge it. The battery recharges automatically through regenerative braking. 

Owing to its small size, the battery in a mild hybrid will often be fully charged after a short journey with a few downhill sections.

What’s the Difference Between a Mild and Full Hybrid Car?

The key difference between a mild hybrid and a full hybrid lies in how much the electric motor can do, and how it is connected to the wheels. A full hybrid, such as the Toyota Prius, has its electric motor connected to the drivetrain in parallel with the engine, meaning either one, or both, can send power to the wheels.

In contrast, a mild hybrid’s electric motor is attached to the engine, and can only assist whilst the engine is running, meaning you cannot drive on electric power alone.

How Much Does a Mild Hybrid Cost to Buy?

The cost of a mild hybrid car varies depending on the model, brand, and features, but generally, mild hybrids tend to be more affordable than full hybrids or plug-in hybrids. You can expect to pay a little premium over a standard petrol or diesel model - usually around £1,000 to £2,000.

For some buying tips on which hybrid could be best for you, why not check out our article on the top hybrids on sale now.

How Much Does a Mild Hybrid Cost to Run?

In terms of running costs, mild hybrids offer better fuel economy than normal ICE cars, but are typically not quite as good as full or PHEV hybrids. Expect to see a modest improvement in fuel economy of around  0-15%. For example, a Ford Fiesta EcoBoost Mild Hybrid could offer up to 55 mpg, compared to around 50 mpg for the older petrol version.

Unfortunately as mild hybrids don't have an EV-only range, the hybrid system is unlikely to help reduce company car tax and VED much, but it might just push the car into a lower band, depending on the alternatives.

Advantages of a Mild-Hybrid Car

• Improved Fuel Efficiency: With the electric motor helping the engine, you can expect better mpg and lower running costs
• Smoother: One of the benefits of an electric motor assisting at lower speeds is that it can make the effect of turbo-lag less noticeable, giving a smoother ride
• Lower Cost: Mild hybrids are usually cheaper to buy than full hybrids or plug-in hybrids
• No Need to Charge: Unlike full hybrids or electric cars, you don’t need to worry about charging a mild hybrid.

Disadvantages of a Mild-Hybrid Car

• No electric-only range: Unlike PHEVs, Mild hybrids cannot drive on the motor alone, meaning you’ll always be using petrol to some extent
• Cost Premium: While more affordable than full hybrids, there is still a small price bump over standard petrol and diesel models
• Limited Impact: The fuel economy improvements are helpful, but they might not be as noteworthy as with full hybrids or EVs

Are Mild Hybrids Worth It?

Mild hybrids are a great option for those looking to dip their toes into the world of hybrid cars without the cost or charging infrastructure needed. They're a solid choice for those who want better fuel efficiency, lower emissions, and a bit of extra help from an electric motor but don’t mind keeping the petrol engine as the main driving force.

I would recommend anyone looking for a petrol car to consider an MHEV, but those looking for an ultimate economy, or electric-only range, should look to plug-in or self-charging hybrids.

Have Your Mild Hybrid Repaired With Bumper

If you already drive a hybrid, or any car for that matter, and you have some issues that need resolving, Bumper's car repair finance can help. Choose from hundreds of nationwide approved garages today.

Author - Joseph Law

Joseph has been writing about cars for over seven years and writing for Bumper for over two, blending his passion for automobiles with a talent for storytelling.

Joseph has written about engineering and cars for Autozilla, Komaspec, and several engineering manufacturers. When he's not writing or tinkering with one of his cars, Joseph dreams of owning an Alfa Romeo 33 Stradale.