A jump start, also known as boost, is a method to start a vehicle with a booted discharge battery. A temporary connection to the battery of another vehicle or to another external power source is established. The external power supply charges the battery of the disabled vehicle and provides some of the power needed to start the engine.
Once the vehicle is started, its normal charging system will recharge, so the auxiliary source can be removed. If the vehicle’s charging system is functional, normal operation of the vehicle will reset the battery charge.
Drivers can carry jumper cables in the event of accidental battery discharge (for example, with headlights or ignition switch on while the engine is running). Safe procedures for connecting and disconnecting cables are provided in the vehicle manual.
The operation of a lead-acid battery can, in the event of overcharging, produce gaseous hydrogen flammable through the electrolysis of the water inside the battery. Load initiation procedures are usually found in the owner’s manual. The recommended sequence of connections is designed to reduce the chance of accidental short-circuit of good battery or ignition of hydrogen gas. The user manuals will display the preferred locations for connecting jumper cables; for example, some vehicles have the battery mounted under a seat or may have a jumper terminal in the engine compartment.
Cables for jumpers should not be used to interconnect between different voltage systems. Connecting together 6 V and 12 V systems can cause damage.
If the dead battery is physically damaged, has a low electrolyte level, is frozen or frozen, a start will not repair the battery. A vehicle with a frozen battery should not start, as the battery may explode.