A jump start, also called a boost, is a method of starting a vehicle with a discharged or dead battery. A temporary connection is made to the battery of another vehicle, or to the Jump Start Battery.

The external supply of electricity recharges the disabled vehicle's battery and provides some of the power needed to crank the engine. Once the vehicle has been started, its normal charging system will recharge, so the auxiliary source can be removed. If the vehicle charging system is functional, normal operation of the vehicle will restore the charge of the battery.