Fiat 500 Mild Hybrid

What is a mild hybrid?

If you’re looking for a car that’s more environmentally friendly, you may want to consider a mild hybrid. But what exactly is a mild hybrid? Here’s everything you need to know.

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By Cazoo editorial team

You might have heard a car being described as a ‘mild-hybrid’, but what does that actually mean? How is it different from a conventional hybrid? And do you have to plug it in? Read on to find out.

What is a mild hybrid?

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

Mild hybrids are the simplest form of hybrid car. They’re different from conventional (or self-charging) hybrids and plug-in hybrids because, unlike those, their electric motor isn’t able to drive the wheels on its own, giving only a small improvement in fuel economy and emissions over a conventional petrol or diesel car.

Fiat 500

How does a mild hybrid work?

The electric motor in mild hybrid cars is a battery-powered ‘starter/generator’ that replaces the starter motor you traditionally find in petrol or diesel cars. It starts the engine and powers most of the car’s electrical equipment. It also stores the energy created when braking and, in most mild hybrids, uses it to help the engine when accelerating. This means that the engine has less work to do, and when an engine has less work to do, it uses less fuel.

Volvo XC60

What’s the difference between a mild hybrid and a conventional hybrid?

All hybrid cars use a battery-powered electrical system to give better fuel economy than they would if they only had an engine. A conventional hybrid has an electric motor that is connected to the wheels and because of that, it can be driven on electricity alone for short distances, eliminating exhaust emissions.

But a mild hybrid’s electrical system isn’t connected to the wheels, so it can’t be driven on electricity alone. You can read more about the differences between mild hybrids, self-charging hybrids and plug-in hybrids here.

Land Rover Discovery Sport

How are a mild hybrid’s batteries recharged?

The batteries that power mild hybrid systems are recharged by ‘regenerative’ braking. When you press the brake pedal, or even just lift off the throttle, the starter-generator reverses the direction of its spin and generates electricity that’s fed back to the batteries.

You don’t have the option of plugging a mild hybrid into a power outlet to recharge its batteries. Only plug-in hybrids and electric cars can be recharged that way.

Ford Puma

What’s it like to drive a mild hybrid?

Driving a mild hybrid feels much the same as driving a ‘normal’ car but there are some differences. Most modern cars have a stop/start system that shuts down the engine when you’re stationary to save fuel. But in a mild hybrid, this function is taken care of by its starter/generator, which usually means you get less of a jolt when the engine starts. Indeed, you may barely even notice it! 

The regenerative braking that recharges the battery can affect how the brakes feel, too. It amplifies the pressure you put on the brake pedal, so the car may slow down more than you expect. Likewise, ‘regen’ can make the car actively slow down, rather than coast, when you lift off the throttle. It might feel a bit strange at first, but you soon get used to it. Finally, some mild hybrid systems are powerful enough to give a noticeable boost in the engine’s power and make it feel more responsive, but you’ll probably only notice the difference if you drive a mild hybrid car immediately after driving a non-mild hybrid model.

Fiat 500

How fuel efficient are mild hybrid cars?

There’s no hard and fast rule on the fuel economy you can expect from a mild hybrid car, but it should be better than a car with a conventional petrol or diesel engine. 

Other than that, the normal principles apply. A large, heavy car with a powerful engine will return lesser fuel economy than a small, light car with lower power, regardless of whether or not it’s a mild hybrid.

Are there any downsides to mild hybrids?

Although mild hybrid systems offer reductions in fuel consumption and carbon dioxide emissions, the reductions aren’t as large as you get with a conventional hybrid or a plug-in hybrid. Mild hybrid cars also don’t give you the option of zero-emissions electric-only power that you get with all plug-in hybrids and most conventional hybrids, either. 

Some mild hybrid models cost a bit more than an equivalent non-mild hybrid version, but as the technology becomes the norm, you may have less  choice on whether or not your petrol or diesel car is a mild hybrid.

Ford Fiesta

What are the upsides to mild hybrids?

In most cases, mild hybrids do give better fuel economy and emit less carbon dioxide, which should lower the amount of road tax you’ll have to pay. They also can make the engine feel smoother and more responsive, which makes driving easier and more enjoyable.

Which car brands make mild hybrids?

Most car brands already have several mild hybrid models in their ranges. Indeed, every new version of the latest BMW 5 Series that isn’t a plug-in hybrid is a mild hybrid, while new cars from Volvo – apart from two versions of the XC40 SUV – are either mild hybrids or plug-in hybrids. Every new Fiat 500 is a mild hybrid, too, although Fiat simply badges the car as a 'hybrid'.

Within the next few years, pretty much every car that isn’t a self-charging or plug-in hybrid, or fully electric will have to be a mild hybrid to meet emissions standards.

Volvo S60

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