A portable vehicle jump starting device can be handy if your car has a dead battery. However, the jump starter won't do much good if it, too, is dead. Fortunately, most vehicle battery jump starters, sometimes referred to as battery chargers, come with several options to keep them charged. How you charge your specific battery jump starter will depend on the brand and item you purchased.
Plug the battery jump starter into a regular wall outlet. Many car battery jump starters and chargers have standard plugs that can connect them to an electrical socket. These batteries charge using electricity, so the process is similar to plugging your cell phone into its wall-charger.
Use your vehicle's A/C adaptor. You can charge many car battery jump starters by attaching them to the A/C adaptor (cigarette lighter) on your vehicle. Similar to charging a cell phone in a car, the jump starter can draw enough power from your A/C outlet to keep a full charge and will be ready when you need it.
Use solar power. Though they are not very common, there are solar-powered car battery chargers that can be used to power your car battery jump starter. These are not typically portable, but they do work for stationary battery charging and jumping.
Check the power level on your car battery jump starter frequently to ensure it has enough charge to jump your battery when you need it.
Charging and working with vehicle batteries can be dangerous. Take proper safety precautions when working with batteries.