i would say it has to be your alternator if you keep getting the battery recharged, and it drains quickly. i work at advance auto parts, and i know that the little machine we bring outside to test the charging system is not accurate. i would say to pull your alternator, and take it inside for testing. the machine inside is very accurate, and will show you how many amps the alternator is putting out, and how much it should put out.

hope this helps ya out.