If you bought a rebuilt alternator, it could be a bad one. Maybe a bad battery too, but doubtful. Rebuilt parts are cheaper but sometimes you get a dud! Otherwise you have something that is staying on and taking lot's of battery power! Take it to where you bought these things and let them take a Volt and Amp meter and test the system ! They can tell with these if your Alt. is putting out enough power to charge the battery and also see if the battery is holding the proper Amperage. It should show at least 13.5 volts in the battery after running ! Take it back !