Jump start (vehicle)

A jump start, also called a boost, is a method of starting a vehicle with a discharged starting battery. A temporary connection is made to the battery of another vehicle, or to some other external power source. 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.

Motorists may carry jumper cables in case of accidental discharge of the vehicle battery (for example, by headlights or ignition switch left on while the engine is not running). Safe procedures for connecting and disconnecting cables are given in the vehicle manual.

Jumper cables, also known as booster cables or jump leads, are a pair of insulated wires of sufficient capacity with alligator clips at each end to interconnect the disabled equipment/vehicle with an auxiliary source, such as another vehicle or equipment with the same system voltage or to another battery. The alligator clips may be covered in insulation to prevent inadvertent shorting. Clips may be made of copper or steel. Alligator clips are generally marked by black (−) and red (+) to indicate the polarity.

Operation of a lead-acid battery may, in case of overcharge, produce flammable hydrogen gas by electrolysis of water inside the battery. Jump start procedures are usually found in the vehicle owner's manual. The recommended sequence of connections is intended to reduce the chance of accidentally shorting the good battery or igniting hydrogen gas. Owner's manuals will show the preferred locations for connection of jumper cables; for example, some vehicles have the battery mounted under a seat, or may have a jumper terminal in the engine compartment.

Jumper cables should not be used to interconnect between different voltage systems. Connecting 6 V and 12 V systems together may cause damage.

If the dead battery is physically damaged, has a low electrolyte level, is decayed or frozen, a jump start will not repair the battery. A vehicle with a frozen battery should not be jump started, as the battery may explode.

A hand-portable battery, equipped with attached cables and charger, can be used similarly to another vehicle's battery. A self-contained jump box contains a battery and connects directly to the battery of the engine that needs a boost. Portable boosters may automatically sense the battery's polarity prior to sending power to the vehicle, eliminating the damage that can result from reversing the connection. There are various portable jump starters that are multi-functional and can be used to charge other electronic devices as well.

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Wikipedia