Car battery chargers slowly restore charge to a flat battery. They use low current to gradually charge the battery. This can take several hours. Battery chargers runs through several charging stages, optimising the charge in the battery. When finished the battery will be fully charged (assuming the battery’s not faulty). A portable car battery starter is simply a small charger you can easily pick up and carry with you. A portable jump starter does not charge your flat battery. It simply provides the high level of current needed to start your car. The jump starter is designed to provide short bursts of very high current. Note: If you want to know more about portable jump starters, go here.