Hydraulic hybrid vehicles, or HHVs use a pressurized fluid power source, along with a conventional internal combustion engine (ICE), to achieve better fuel economy and reductions in harmful emissions. They capture and reuse 70–80% of the vehicle's braking/decelerating energy compared to 55% for 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. Hydraulic hybrid vehicle systems can also weigh less than electric systems, due to the high weight of the batteries. This can lead to a lower impact on payload capacity, especially for heavy vehicle classes.