MHEV (Mild Hybrid Electric Vehicle)
Light hybrid system with a secondary 48 V network that assists the engine on acceleration and recovers energy on braking.
MHEV (Mild Hybrid Electric Vehicle) is a "light" hybrid: the combustion engine is the only one that moves the car, but a 48 V (non-traction) electrical system assists during starts, transitions and acceleration, and recovers energy during braking. It reduces fuel consumption by 8-15% in mixed driving compared with the same non-hybridised engine. It uses a compact 8-15 Ah lithium battery at 48 V (sealed module, not user-replaceable) and keeps the conventional 12 V battery to feed accessories. Brands with widespread 48 V MHEV: Audi (broad range since the A8 D5 in 2017), BMW (progressive 48 V rollout between 2019 and 2021), Mercedes (EQ Boost), Land Rover, and much of the VAG group.
Mazda and some Asian brands use mild-hybrid systems at 24 V rather than 48 V (Mazda "M Hybrid"). It is NOT the same as a full hybrid (HEV), which can move the car under electric power. The 12 V battery the user replaces is still a conventional AGM or EFB — the mild-hybrid system is separate.