Hi Alex, you can start and run one of these without a battery. There is one proviso which is that the main field winding is initially energized by the battery during start up, this should not be a problem as once the head starts to generate, 24 volt DC is fed into the main field winding to maintain it`s magnetism. If you let the generator stop with a load attached you will loose the magnetism in the field winding and have to either flash it or use the batteries to start the generator.
Bob