Hydraulic hybrid vehicles, or
HHVs use a pressurized fluid power source, along with a conventional
internal combustion engine (ICE), to achieve better
fuel economy. They capture and reuse 70%-80% of the vehicle's braking/decelerating energy compared to 25 or electric hybrids. For trucks and buses, this can also be less expensive than electric systems, due to the price of
batteries required for the latter.