The characteristics of a good battery jump starter are having additional features built in that go beyond just jumping the car and having enough power to start a completely drained battery. A good battery jump starter is also safe and easy to use.
Battery jump starters come in many different sizes and styles, and they also make use of different technologies. A less expensive battery jump starter might lack capability and reliability. Although at the heart of every jump starter there is a battery powerful enough to start a car, a good battery jump starter has additional features built in that go beyond just starting the vehicle.
A good battery jump starter has a built-in charger. The charger makes sure that the jump starter is always available when it is needed. A good battery jump starter also has plenty of power. In emergency situations where the battery is completely drained, like leaving the lights on at the airport while on vacation, a lesser-powered battery jump starter might not do the job. A more powerful jump starter has the extra ability to revive completely dead batteries.
Being safe and easy to use is another characteristic of a good battery jump starter. The cables should be easily accessible, and a good jump starter even comes with alligator clamps for the battery terminals.