What Are the Disadvantages of a Mild Hybrid Car?

June 13, 2024

Mild-hybrid cars, or MHEVs, represent a bridge between conventional combustion engines and fully electric vehicles, offering a blend of conventional and electric propulsion technologies that enhance fuel efficiency and reduce emissions without the need for plugging in. These vehicles are becoming increasingly popular for their ability to provide better fuel economy with a minimal increase in vehicle complexity and cost.

"Roter Audi RS 7 Sportback C8, V8-Mild-Hybrid, Heckansicht" by verchmarco is licensed under CC BY 2.0. To view a copy of this license, visit https://creativecommons.org/licenses/by/2.0/.

Electrical System

Mild-hybrid cars typically use a 48-volt electrical system, which is higher than that of traditional combustion engines. This system powers components that were previously powered by the engine, making the engine operate more efficiently. The higher voltage system is key to enabling mild-hybrids to capture and utilize more energy than conventional systems.


Mild-hybrid cars provide gentle electrical assistance rather than full electric propulsion. Unlike regular hybrids and plug-in hybrids, MHEVs cannot be driven on electric power alone. The electric motor in MHEVs assists the engine, especially under hard acceleration, and helps improve the smoothness of the stop-start system. Vehicles with mild-hybrid technology use electric motors for boosting and regenerative braking but never drive purely on electric power.

Regenerative Braking

MHEVs use regenerative braking to capture energy during braking or coasting. This captured energy is converted into electricity and stored in a lithium-ion battery. The stored energy is then used to provide additional assistance to the engine when needed, making the vehicle more efficient.


Mild-hybrid technology can make a car approximately 15% more efficient compared to conventional cars. This improvement is achieved by reducing the engine load through electrical assistance, utilizing regenerative braking, and optimizing the stop-start system, all of which contribute to lower fuel consumption and fewer emissions.

Examples and Manufacturers

The Ford Puma serves as a prime example of mild-hybrid technology enhancing both economy and performance. This model, along with versions of the Ford Focus and Ford Kuga, uses a 1.0-litre three-cylinder mild-hybrid petrol engine. Ford's system continuously monitors driving habits to optimize battery charging and engine assistance. Additionally, mild-hybrid systems can vary slightly depending on the car manufacturer’s design and functionality, though the core principles remain similar.

Overall, mild-hybrid vehicles offer a practical and efficient step towards greener transportation, leveraging familiar technologies to deliver notable improvements in fuel economy and emissions without the need for fundamental changes in driving habits or infrastructure.

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