A genset trailer is a range extending device for use with battery electric vehicles consisting of an internal combustion engine and an electric generator (collectively called a genset). They run on traditional fuels such as gasoline or diesel and are sized to provide the continuous power requirements for the vehicle they are used with. Most small to midsized passenger vehicles would require 15 to 20 kW (20 to 27 hp) for unlimited freeway travel using fuel. Larger vehicles could require 30 kW (40 hp) or more of power depending on how heavy or un-aerodynamic they happen to be. This essentially converts an electric vehicle into a series-hybrid.