There are many signs of a weak battery—dim lights, electrical component issues, battery warning light—but if your engine won’t turn on at all, your battery is probably dead. This often happens when headlights or the ignition switch is left on while the car is not running.
The tell-tale sign that you have a dead battery is if the car makes a clicking noise when you turn the ignition, but it won’t start.
Jump starter, also called a boost, is a method of starting a vehicle that has a discharged or dead 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.