What Is a 48-Volt Mild-Hybrid System?

This technology assists the engine to improve fuel economy.

Sami Haj-Assaad | 

Feb 2, 2024 | 2 min read

Audi

While automakers are hard at work developing electric vehicles for a greener (and quieter) future, they know that it'll take the public a while to move away from internal combustion entirely. In the meantime, many have sought to make their traditional powertrains more efficient with what's known in the industry as 48-volt mild hybridization. Typically, such a system — consisting of a small motor and a 48-volt battery — assists with the engine's stop/start function and provides power to the auxiliary features of a car, thus reducing the load on the engine and improving fuel efficiency. It can also boost torque output at low speeds.

How Do Full Hybrids Differ From Mild Hybrids?

Much like mild hybrids, full hybrids pair an internal-combustion engine with a small battery and an electric motor. The engine serves as the primary power source in both cases, and each system uses energy from a regenerative braking system to charge its battery.

Traditional hybrid vehicles, however, can also travel moderate distances solely on electricity — something mild hybrids can't do. This requires a relatively large battery and powerful motor, which add weight, expense, and complexity to the powertrain.

Pros and Cons of 48-Volt Technology

The biggest advantage of a 48-volt mild-hybrid system is that it's small — at least compared with a full hybrid setup. As such, automakers can integrate it into an existing powertrain with relative ease and reap the reward of improved efficiency. Further, the small size of a mild-hybrid system means it probably won't impact interior space or driving dynamics as the components of some full hybrids do.

However, full hybrids have the edge in efficiency, given that they can run on electric power alone. When they do so, moreover, they're generally very quiet. And because full hybrids use larger motors and batteries than 48-volt systems, they can supply the engine with more power.

48-Volt Technology in Action

Automakers such as Audi, BMW, Land Rover, Mercedes, Porsche, Stellantis, and Volvo employ mild hybridization in various models. In addition to powering a car's electrical components (e.g., lighting, infotainment, windshield wipers, etc.) and helping make start/stop operation seamless, such systems may also serve other functions.

For example, to enhance throttle response, the 48-volt system in the 2024 Mercedes C-Class runs an electric motor to spin a turbocharger before the exhaust gas kicks in. And Audi uses its system in the A8 to power its active suspension and rear-wheel steering, enabling a smooth ride and improving handling.

Sami Haj-Assaad

Sami Haj-Assaad is an award-winning automotive journalist who has contributed to several automotive, electric vehicle, luxury lifestyle, and technology publications. His work isn't just limited to the written word, as he's also hosted YouTube videos and podcasts. Having grown up in the '90s, he has a strong sense of attachment to that era's style, though he also loves to geek out about the modern, futuristic tech and powertrains rolling out today.