In the case of the Toyota Prius Plug-in, Ford Fusion and C-Max Energi models, the cars use a powertrain much like a traditional hybrid but feature a larger battery. Charge these cars up and you get a limited range of continuous emissions free driving. Once that range is depleted, the car acts like a normal hybrid, using minimal fuel and recapturing energy from deceleration to use with the car’s electric motor.
All of these options are capable of staying fuel-free within the confines of your daily commute, should you charge them every night. However, you can use the secondary power source to tackle longer trips.