What is a mild hybrid car?

A boost to fuel economy without the cost of a full hybrid car: why mild hybrid technology could well be coming to your next car.

BuyaCar team
Nov 11, 2020

As the country becomes ever more concerned about an eco-friendly future, consumer preferences are heading in a greener direction, affecting the type of cars many drivers choose. Couple that with government initiatives to crack down on fossil fuel emissions and climate change and car manufacturers have their work cut out to adjust to a new set of needs.

Over the last decade we have seen the motoring industry take sharp turn towards efficiency, fitting hybrid technology designed to reduce exhaust emissions and limit the impact on the environment into a broader range of vehicles. Hybrid cars don't just come in one format, though.

In the 2020s drivers can choose between everything from more affordable hybrids that offer a small electric boost to reduce fuel consumption to plug-in models that have large batteries allowing them to complete many journeys solely on electric power - if they're charged regularly.

So, there are various types of hybrid car, but mild hybrids are designed to remain as close to traditional cars as possible in terms of functionality. This means they are the most affordable and least economical types of hybrid. Where plug-in hybrids have large battery packs that need to be charged regularly for the best fuel economy, you may not notice that a mild hybrid is a hybrid unless you read the manual.

As a result, if you're after the most affordable hybrid car that is potentially a little more economical than non-hybrid equivalents, but don't want to pay a premium or worry about having to charge the car, a mild hybrid car could be perfect for you.

What is a mild hybrid car?

Mild hybrids have a slightly bigger battery than normal cars. This might not sound very exciting, but the extra electrical capacity can provide enough energy to power a small electric motor that supplements the power of the engine under acceleration.

This minor assistance helps to reduce the stress on the petrol or diesel engine, thereby reducing the amount of fuel it burns and improving efficiency. This leads to better fuel economy - meaning that your fuel bills are a littl lower than they would otherwise be - and you get lower CO2 emissions from the exhaust.

The best systems also allow the engine to be switched off for short periods while the car is travelling at a steady speed, further improving efficiency.


Cheapest type of hybrid car
Some fuel economy benefits
Performance improvements


Limited improvement in efficiency
More expensive than non-hybrid cars
Small number of models so far

How mild hybrid cars work

Mild hybrid cars usually have a 48 volt battery that can deliver more power than the standard 12 volt battery that’s under the bonnet of most cars. The example of the Kia Sportage, above, shows the battery at the back of the car.

These batteries can store more energy than a conventional car but they are much smaller than those in other types of hybrid car. A Toyota Prius, for example, can store three times as much electricity as an Audi A7 or Kia Sportage mild hybrid.

The extra capability still comes in useful to drive a small motor next to the car’s engine (labelled mild hybrid starter and generator, above). In some systems, such as those used by Kia, the battery powers the motor under acceleration, reducing the need to work the engine hard, which is particularly inefficient.

In other mild hybrids, the motor can keep the car going at a steady speed, which doesn’t require a great deal of energy, allowing the engine to be switched off - for up to 40 seconds in mild hybrid-powered Audis. During this time the car isn't burning any fuel - again reducing your fuel bills and cutting the emissions of the car.

The batteries recover energy as the car slows down and brakes, shown by the yellow arrows in the diagram above. They can also be recharged during steady driving, when the car calculates that it is efficient to do so. This ensures that the hybrid tech causes the least possible drain on the petrol or diesel engine and provides the greatest electric boost possible.

Used mild hybrid cars

Of all the hybrid options on the market, mild hybrids make up the smallest percentage at the turn of the 2020s. Due to their 'mild' nature, their impact on efficiency is much less pronounced, and while prices for mild hybrids remain higher than regular petrol or diesel alternatives, they aren't as expensive as plug-in hybrids, which feature much larger battery packs and more substantial electric motors.

Used car deals. however, see that price gap close almost completely, with just a few hundred pounds proving the difference. So if you fancy saving yourself a bit of fuel money each month, a used mild hybrid might be a convenient way to go about it. Used mild hybrids are likely to become available in ever greater numbers as this tech is integrated into ever more new cars.

Common examples of mild hybrid models available now are 'MHEV' versions of the Mazda 2 and Mazda 3, a number of Audi 'S' models, and several versions of the Kia Sportage and Hyundai Tucson. Suzuki also implements mild hybrid technology in the Swift and Ignis ranges, in models which are labelled 'SHVS'.


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