Most modern motorcycles rely on a battery and a charging system to keep the motor running. These electrical systems provide the spark that ignites the fuel as well as providing the power that keeps the lights on. A magneto is completely separated from the rest of the electrical system and will allow the motorcycle to run even if the battery fails. This is the same type of system you will find on most lawn mowers, trimmers, or chain saws. Once the engine is started, it will continue to run on it's own.