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A capacitor jump starter is a gadget which can charge your vehicle in the event of a power outage—but more importantly these best capacitor jump starters can give you an out-of-car boost when you need charging. For example, there may be a length of unused electrical line next to your car, or you might have a generator in your house. Connecting a capacitor to this power source can really crank up the surge that's needed to start a dead car battery.