Were you reading the same 6.5 volts both at the generator and at the battery? If so that means the generator is putting out enough to close the contacts of the regulator and is charging, though maybe not much. As long as the cutout contacts of the regulator or closed the gen and battery will be the same voltage. If you are sure you grounded the terminal when it went full discharge, either the generator needs polarized, or the ammeter is wired backward. Here is a trouble shooting chart compliments of Farmall Bob.