Here is a list of some basic questions about a jump starter

Q. What is the ideal use for a jump starter?

A. A jump starter performs strongly when a vehicle’s battery needs an extra boost
because a light or radio was left on, or when a vehicle has been sitting for a long period
of time. A jump starter will start vehicles without any other batteries present but
the primary use is for an extra boost.

Q. Will a jump starter start every vehicle?

A. No. In addition to a dead battery, a car may have other mechanical problems that would prevent a jump starter from starting the vehicle.

Q. How often should I recharge a jump starter?

A. To maximize battery life, charging after use is recommended. A jump starter should not be left in a discharged state. The battery in a jump-starter has no memory
problems and should not be treated as a rechargeable tool (cordless drills, camcorders,
etc.).
 

Q. How many jump starts can I get from  a jump starter before recharging?
 

A. A large number of factors affect this answer including the following: the length of time for each jump start, the charge level of the original battery, the length of time between jump starts, the temperature of the vehicles being jump-started (winter cold makes fordifficult starting), the size of the engines (4-cycl, 6-cycl, 8-cycl, etc.), the mechanical condition of the engine and starter, and more. These factors must all be weighed on an individual basis before an accurate answer can be given. It’s feasible to get 10-30 starts (individual’s results will differ) from a single charge, but this violates the rule of immediate charging a