Mild hybrid cars: Everything you need to know
Last updated September 8th, 2023
If you have even a mild interest in the automotive world, you’ll probably be familiar with some of the different types of electric cars, such as fully electric vehicles (EVs) or plug-in hybrid electric vehicles (PHEVs).
You might also be familiar with mild hybrid electric vehicles (MHEV) - a variant of the hybrid car that is becoming increasingly popular on the roads today.
In this guide, we will explain what constitutes a mild hybrid - and how they differ from other electric car varieties. We’ll also cover the benefits of mild hybrids, including their eco-credentials and battery life.
Whether you’re preparing to sell your car and make the switch to a mild hybrid model or simply wish to learn more about the technology, our guide will tell you everything you need to know.
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What is a mild hybrid car?
A mild hybrid electric vehicle (MHEV) utilises a battery-powered electric motor to support a petrol or diesel engine. This means that MHEVs offer improved efficiency and lower emissions compared to their traditionally-fuelled counterparts.
Mild hybrid electric vehicles also utilise regenerative braking to charge the battery whilst in use. Therefore, unlike EVs, MHEVs don’t require charging from an external source.
How does a mild hybrid system work?
Mild hybrids utilise both an electric motor and a 48-volt battery with a petrol or diesel engine. The electric motor integrates with the engine to use stored energy, which provides extra torque.
The system has the capability to monitor the usage of the vehicle and therefore knows when to charge the battery - or alternatively, use it. Mild hybrid electric vehicles utilise regenerative braking to charge the battery when in use. Therefore, this energy is stored in the 48-volt battery, ready for use.
Is it worth buying a mild hybrid car?
Depending on your priorities, a mild hybrid car could be a great choice:
- MHEVs reduce engine load, providing a smoother ride.
- The battery in an MHEV can provide greater torque due to smoother acceleration.
- MHEVs produce less emissions than equivalent pure petrol or diesel vehicles and are cheaper to run.
- MHEVs typically retail for less than PHEVs and EVs.
- MHEVs tend to be lighter than PHEVs.
- You won’t have range anxiety thanks to the backup petrol or diesel engine.
However, there are also several potential drawbacks to consider:
- MHEVs cannot run on electric power alone - and therefore aren’t as efficient as PHEVs and EVs.
- There are no Government Grants available for MHEVs (unlike EVs).
- MHEVs still produce CO2, which may deter eco-conscious drivers.
- MHEV drivers will have to pay daily fees if they travel in London’s Congestion Charge Zone or Clean Air Zones (such as those operating in Bath, Bristol and Birmingham).
What is the difference between a mild hybrid car and a hybrid?
You may be wondering how mild hybrids differ from standard hybrid cars:
- A plug-in hybrid vehicle (PHEV) has a much smaller fuel engine and can be powered exclusively by a large battery pack.
- A mild hybrid electric vehicle (MHEV) blends a traditional fuel engine and electric power meaning it does not have to be plugged in. Instead, MHEVs have a small electric motor, which is attached to a petrol or diesel engine. The small electric motor provides a boost when accelerating.
Are all mild hybrids the same?
There is a vast range of MHEVs on the market - and some models feature more sophisticated technology than others.
For example, the Audi Q8 has a feature which improves economy by working with the car’s cruise control system (meaning that it slows down when approaching corners and roundabouts, allowing it to utilise the energy collected from regenerative braking).
How eco-friendly are mild hybrid cars?
Mild hybrids aren’t as eco-friendly as many traditional hybrid cars:
- For instance, the Ford Puma 1.0 Ecoboost 125 MHEV’s CO2 emissions figure of 123g/km compares favourably with most standard small SUVs.
- However, it is still undeniably higher than the PHEV Mini Countryman's 40g/km.
Although MHEVs offer an eco-friendly alternative to typical petrol and diesel cars, they cannot compete with PHEVs and EVs.
What are the other types of hybrids?
Other hybrid cars on the market include:
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Parallel hybrids
A parallel hybrid car’s wheels can be powered by the engine, the electric motor or both power sources. At speeds of up to 15mph, only the electric motor is used for power, which makes parallel hybrids particularly efficient for city driving.
The petrol engine cuts in when the speed increases (or under hard acceleration). When you decelerate or use the brakes, the regenerative braking system garners electricity, storing it in the battery for later use. However, parallel hybrids cars can only run on electricity for up to 1.25 miles.
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Range-extended hybrids
Range-extended hybrid cars differ from regular hybrids as their combustion engines act mainly as generators, producing electricity to power the electric motors driving the wheels.
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Plug-in hybrids
As their name suggests, PHEVs can be plugged into an electrical outlet to recharge their batteries.
Although PHEVs have conventional engines, they also have larger batteries than the average mild hybrid. What’s more, unlike MHEVs, they can travel on electric power alone, which reduces running costs when they are charged regularly.
Frequently Asked Questions
MHEVs start the engine, whilst powering the other electrical systems. Therefore, the engine expends more energy driving the wheels, which translates to greater fuel efficiency.
Yes, a mild hybrid can be considered a self-charging car. MHEVs don’t require charging at all because the battery is much smaller than a full hybrid’s. Instead, the regenerative braking powers the battery. Therefore, the battery recharges every time you brake.
Leading MHEV manufacturers such as Honda and Toyota state that hybrid batteries last between 80,000 and 100,000 miles.
However, some hybrid car drivers have claimed their batteries lasted up to 200,000 miles. (An EV’s battery life is typically between 100,000 and 200,000 miles – or 10-20 years.)
MHEVs are often placed in lower car tax bands than traditionally-fuelled models due to their lower CO2 emissions.
MHEVs tend to be placed in lower car tax bands than traditional petrol and diesel vehicles. However, they are not zero-emission vehicles. Therefore, MHEVs are taxed at a higher rate than EVs.
If you have a mild hybrid as a company car, you will have to pay benefit-in-kind (BIK) tax on it. Whilst the current BIK rate for EVs is 2%, you may have to pay a slightly higher rate for a MHEV, depending on its CO2 emission level.