2002 Buick Century Battery Will Not Stay Charged

My battery will not stay charged. I have replaced the battery twice, so the battery is new. I have also replaced the alternator with this problem came up because it was weak. Even after a brand new alternator which I also took in to get tested and a brand new battery, the car still will not keep the battery charged. Is there something that could be keeping this from happening like a fusible link, or could I just bypass all the wires and hook up a cable straight from the battery to the alternator with no side effects? I am assuming that there is an electrical problem between the alternator and the battery since both are brand new and working. Thanks for your time.