Definition of Jump Start

You come out to the parking lot after shopping or perhaps a long day at work. You put the key in the ignition, turn it and--nothing happens. It doesn't even "try" to start. You get that sinking feeling as you realize that you forgot to turn the headlights off this morning. Now your battery is dead. But, there is hope. You just need a jump start. But, what exactly is a jump start and how does it work?

Definition of a Jump Start

A jump start is the process of using the power from one car to start the engine of another car that has a dead battery. Using jumper cables, you "jump" power from a "live" car to the car with the dead battery.

How It's Done

Jump starting a car with a dead battery first requires another car with a live battery. You also need jumper cables. Simply have the "live" car started and use the jumper cables to connect the two batteries. Be sure to connect the battery terminals correctly. You need to connect the red terminal on the "live" battery to the red terminal on the dead battery, and the black terminal on the live battery should be connected to the black terminal on the dead battery. Once the terminals are connected correctly, start the dead car. Once the dead car starts, disconnect the jumper cables and close the hoods of both cars. You will need to drive the car with the "dead" battery for about twenty minutes to let it charge fully.

How It Works

The power for the jump start actually doesn't flow just from battery to battery. While a battery is necessary for starting a car, once the car is running, the alternator recharges the battery. So while the cars are connected battery to battery, the other car's alternator is charging the dead battery, giving it enough power to start the car. The alternator is also what normally powers headlights and all other electrical components in the car. If the headlights are left on after the engine is shut off, the headlights will run off the battery and thus run the battery down.
But, when you use one car to jump start another, the dead car charges from the running car's alternator and this gives the dead car the boost it needs to start. Once the dead car is started and running, the alternator will start to charge the dead battery.

Other Alternatives

Batteries may go dead for different reasons. First of all, batteries have a useful life of about five or six years. In addition to, for example, leaving the headlights on, other factors that affect battery life are extreme cold or a bad alternator. Whatever the cause of a dead battery, you may at some point find yourself stranded without another vehicle nearby to help when you need it. For those cases, many companies make portable battery jumpers that substitute for another car. These battery jumpers have their own cables that you attach to your battery and the jumper provides enough power to start your car.

How to Avoid Needing a Jump Start

Always be sure to turn off your headlights when you turn off the ignition. Avoid just turning the key on to listen to the radio or run the fan when the engine is not running. Check your serpentine belt or alternator belt and the battery terminals for acid deposits when having your vehicle serviced. Be aware of your battery's age and life expectancy. If possible, keep your car in a garage, especially in winter when the temperatures reach extreme cold.