- does your generator have DC out put - or it is a self start generator. If it has a battery to start engine. a battery can be charged without problems.
or through DC plug before that do check what is voltage at DC plugs 12 VD or 24 DC using DVM
check the Specific gravity of the each cell in the battery using a hydrometer - if that is correct step 2 is - when generating is running use a volt meter disconnect positive terminal from battery. select DC voltage on DVM connect red probe to removed cable and negative probe to battery terminal if the reading is between 14.1 ~ 14.5 volts steady the charging voltage is perfect from the generator, and battery will be charged.