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
Mar 19, 2020

As mind-sets are changing and societal norms evolving towards a more eco-friendly future, consumer preferences are heading in a greener direction. Couple that with government initiatives to crack down on fossil fuel emissions and climate change and car manufacturers have got 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, introducing hybrid technology designed to reduce exhaust emissions and limit the impact on the environment.

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. Where plug-in hybrids require batteries to be charged regularly, a mild hybrid will hardly show itself to be a hybrid unless you read the manual.

So these cars might well be the preferred choice for many drivers who don't want to be dealing with charging and the like, but still have an interest in reducing their fuel dependency and shrinking their carbon footprint.

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 combustion engine, whereby reducing the fuel it burns and improving efficiency. This leads to better fuel economy and 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.


βœ” Cheapest hybrid tech
βœ” Some fuel economy benefits
βœ” 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 other hybrid cars. 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 rev the engine, which is particularly inefficient.

In others, 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.

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.

Used mild hybrid cars

Of all the hybrid options on the market nowadays, mild-hybrids make up the smallest percentage. Due to their 'mild' nature, their impact on efficiency is much less pronounced, and while prices remain higher than regular petrol or diesel alternatives, they aren't as expensive as more intrusive plug-in hybrids. Used car deals especially 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.

Common examples can be found in Mazda 2 and Mazda 3 MHEV models, Audi 'S' models, the Kia Sportage and Hyundai Tucson. Suzuki also implements mild-hybrid technology in the Swift and Ignis ranges labelled SHVS.


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