Hybrid cars are powered by an internal combustion engine (petrol or diesel) and one or more electric motors, which is powered by energy stored in the electric batteries.
There are three main types of hybrid:
mild (or MHEV) use the electric motor to support the engine,
‘full’ hybrids (or HEVs) alternate between the internal combustion engine and the battery and can run for short distances on electric power alone,
plug-in hybrids (or PHEVs) have bigger batteries and can run for longer distances (typically around 20-30 miles) using the electric motor(s) alone.