There are some cigarette lighter jump starters available on the market, although generally they are useless to immediately start a car with a completely dead battery. In order to start a dead car battery, the vehicle will need a huge amount of electrical current. The car with the dead battery draws a tremendous amount of amperage from the car with the good battery. Cigarette lighter circuits are typically fused at 10A when you'll usually need around 350A or more to crank the engine. If you car's battery isn't completely discharged, and only in this occasion, a cigarette lighter jump starter may help if you leave it connected at least for some minutes, as it will feed your battery with some juice that may be enough to start the engine.