I am guessing, but maybe the generator on your aircraft is a back-up stand alone DC source used to run vital standby instruments in the event of a major electrical failure of the alternator and battery?
Or does your aircraft have electronic displays only, which if the normal DC power failed would leave you with nothing - hence the need for a back-up DC source?
I would need to see the aircraft's electrical schematic to confirm this - can you print it here?