What is a mild hybrid car?

  • How does a mild hybrid car work...
  • ... and how is it different to a regular hybrid?
  • Parkers explains the tech

If you’re in the market for a new car then there’s no avoiding the marketing-speak and techno-babble that manufacturers will use to try and convince you their new model is more efficient or better for the environment than its rivals. Mild hybrid is just such a term, and you’ll see it popping up in cars from superminis to SUVs.

But what makes a mild hybrid car different to a regular hybrid – and does it really mean anything for you, the owner? Read on to find out.

If you’re interested in different hybrids, click here to find out more about traditional (sometimes known as ‘self-charging’ hybrids) and plug-in hybrids (or PHEVs).

>> What is a hybrid car?

>> What is a plug-in hybrid?

>> The Parkers guide to home chargers

What is a mild hybrid system?

As the hybrid part of its name suggests, a mild hybrid car blends a combustion engine – whether petrol or diesel – with some assistance from an electric motor and battery pack. This electric portion helps improve fuel economy as well as engine response.

Ford Focus mild hybrid

But that’s where the ‘mild’ part comes in, because these cars are somewhat of a stopgap between a full hybrid system and a conventional car. Mild hybrid cars use a very small electric motor and battery pack, which are not capable of powering the car on electric power alone like a traditional hybrid.

As a result, a mild hybrid works more like an advanced version of an engine stop/start system. The electrical assistance allows the car’s engine to switch off earlier, usually while you’re coasting to a stop instead of when you’ve come to a complete halt.

They also improve the engine’s response, helping it to start up more quickly and occasionally filling in gaps in power at low revs.

How does a mild hybrid work?

Different manufacturers have different systems, which makes classifying them quite tricky indeed. Most affordable mild hybrid cars, though, use what’s called a ‘starter-generator’ – a beefy motor that starts the car’s engine but can also capture energy as the car slows down. It’s this regeneration that charges the mild hybrid’s dinky battery pack.

Mild hybrid diagram

At the other end of the scale, mild hybrid systems found on large executive cars may underpin their batteries and motors with upgraded, 48-volt electrical systems. This allows for the starter-generator to play a greater role in helping the engine out, and lets it shut off earlier when coasting to a stop.

Driving a mild hybrid car isn’t anything like a full hybrid. In fact, there’s no difference to the end user – since the car shuffles its power sources entirely by itself, you can just get in and drive as normal. Because the electric motor only boosts the engine, too, it means there’s no need for a special kind of gearbox – mild hybrid cars can even have manual gearboxes.

What are the advantages and disadvantages?

For manufacturers, it’s clear – they get to badge their cars as hybrids, while only fitting comparatively low-cost hardware. We think this is a little dishonest, and it’s important that buyers know despite the ‘hybrid’ in the name, a mild hybrid car doesn’t have the same capability as a self-charging or plug-in hybrid.

There are genuine benefits, though, particularly to fuel economy and carbon dioxide emissions – both important factors to consider when buying a car. Mild hybrid systems also don’t take up anywhere near as much space as full hybrid systems – without such a large battery pack to accommodate, they don’t suffer from the same reduced luggage space as many hybrid rivals.

Fiat 500 mild hybrid

As for the disadvantages, some systems work better than others – and the worst make the car less pleasant to drive, with jerky response at low speed. It’s also a shame that mild hybrid drivers won’t get to experience the smooth, silent running of a hybrid or plug-in hybrid in fully electric mode, nor will they enjoy those model’s extraordinarily low fuel consumption or CO2 emissions and associated company car benefits.

Which manufacturers use mild hybrid systems?

More and more manufacturers are opting to fit a mild hybrid system to their cars, to the point where in a few short years, it might be quite difficult to find a car without one.

Ecoboost hybrid badge

What’s annoying and a bit confusing is that there’s no standard way to refer to a mild hybrid car, so it’s very important to check to make sure you know what you’re getting. Ford, for example, badges them as ‘EcoBoost hybrid’ – which could easily lead someone into believing they’re getting more capability than they actually are.

Other manufacturers don’t even mention the word hybrid, such as Volkswagen with its e-TSI mild hybrid engines or Mercedes-Benz with its EQ Boost tech. 'MHEV' (standing for mild hybrid electric vehicle) is another common badging. The bottom line? Make sure you read the Parkers reviews of the cars you’re considering – we’ll always mention what kind of hybrid systems they have, if any – and ask the salesperson plenty of questions.

Further reading:

> The best hybrid cars to buy

> The best hybrid SUVs

> The best electric cars