Like most bikes, the Enfield electrical system is designed to run off the battery. This will provide relatively consistent power to components such as lights, which in turn provides constant, even performance regardless of engine RPM. The charging system (alternator/generator) then charges the battery. Low, no, or dead battery equals no spark/no go.
Magnetos provide power to spark, but at starting or low RPM spark is weak. So starting can be difficult. When running, a magneto will power lights, but intensity varies with RPM and lights tend to burn out at high RPM. That is why most bikes no longer have magnetos.