Pusher trailer
A pusher trailer is a device attached to the rear of a vehicle or bike that provides force to assist the vehicle. For bikes. Electric. Electric pusher trailers use energy stored in a battery, typically of lithium ion or sealed lead acid chemistry, to provide power. Two wheel and one wheel designs are common. Gas. Gas powered pusher trailers typically employ a two or four stroke internal combustion engine to provide power. For cars. Pusher trailers are gasoline, diesel or electric fueled trailers with a traditional internal combustion engine (petroleum engines) and transmission which can be hitched up  to battery electric vehicles and run from the cockpit to give the vehicle increased range. The trailer provides ground traction through the wheels to push the trailer forward, and by default, the electric vehicle as well. In this way, a trip beyond the normal range of the EV can be undertaken without stopping for recharging. Some types of articulated bus have the engine (and propulsion) in the rear section.