Fiat 500 Mild Hybrid

What is a mild hybrid car?

If you’re looking for a car that’s more environmentally friendly, you may want to consider a mild hybrid. But what exactly is that? 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 other types of hybrid cars? 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 a mild-hybrid electric vehicle, or MHEV) has a petrol or diesel combustion engine and a small, battery-powered electric motor that helps improve your fuel economy while reducing your car’s carbon dioxide emissions.

Mild hybrids are the simplest form of hybrid car. They’re different from conventional hybrids (often known as full hybrids or ‘self-charging’ hybrids) and plug-in hybrids because the electric motor doesn’t drive the wheels directly. Instead, a mild hybrid’s job is to help the engine, particularly under acceleration. This can improve your car’s fuel economy and reduce its exhaust emissions compared with a conventional petrol or diesel car.

Different car manufacturers have mild-hybrid systems that work in slightly different ways, but they all follow this broad principle. Because mild-hybrid cars are simpler than other hybrid systems, they’re usually more affordable to buy.

Fiat 500

How does a mild hybrid work?

The electric motor in a mild hybrid car is a battery-powered ‘starter/generator’ that replaces the starter motor and alternator you’d traditionally find in a petrol or diesel car.

The generator starts the engine and powers most of the car’s electrical equipment. It also stores the energy created when you brake and, in most mild hybrids, uses that energy to help the engine when accelerating. This means that the engine has less work to do, which means it uses less fuel.

Volvo XC40

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

All hybrid cars use battery-powered electrical systems to give better fuel economy than if they only had engines. A conventional full hybrid has an electric motor connected directly to the wheel, which in most cases means the car can be driven on electricity alone for short distances, with no exhaust emissions.

But a mild hybrid’s electrical system isn’t connected to the wheels, so you can’t drive it solely on electric power. 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. That means that 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, which is fed back to the batteries.

You don’t plug a mild hybrid into a power outlet to recharge its batteries. Only plug-in hybrids and electric cars are 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 small differences. Most modern cars have a stop/start system, which 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 – you may not even notice it.

The regenerative braking that recharges the battery can affect how the brakes feel, and the car may slow down more than you expect when you press the brake or lift off the accelerator. It might feel a bit strange at first, but you soon get used to it.

Some mild hybrid systems are powerful enough to give a boost in the engine’s acceleration, but you’ll probably only notice the difference if you drive a mild-hybrid car immediately after driving a regular 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 get through more fuel than a small, light car with lower power, regardless of whether it’s a mild hybrid.

Are there any downsides to mild hybrids?

Although mild-hybrid systems reduce your car’s 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-emission, electric-only power, which you get with all plug-in hybrids and most full hybrids.

Some mild-hybrid models cost a bit more than an equivalent non-mild hybrid version, but the technology is fast becoming the norm for new cars.

Ford Fiesta

What are the upsides to mild hybrids?

In most cases, mild hybrids give you better fuel economy and emit less carbon dioxide, which should lower the amount of Vehicle Excise Duty (car tax) you’ll have to pay. The engine usually feels 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. For example, every new version of the latest BMW 5 Series that isn’t a plug-in hybrid is a mild hybrid, while almost all new cars from Volvo are either mild hybrids, plug-in hybrids or full-electric cars. Every new Fiat 500 is a mild hybrid too, although Fiat badges the car simply as a 'hybrid'.

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

Volvo S60

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