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.