1999 Chrysler Sebring Battery?

[63 chevy]

Well I hae a 1999 Chrysler Sebring and Ive been having problems with the battery. It keeps killing the battery. Ive replase the battery because I thought that might of been the problem but it only help for about one month, then i stop the car for about another two moths. When I try to start it the battery was dead and Ive been driving it like that but it keeps killing it. I took the car to a Auto Parts store were they could check my Alternator and they said that it was good. I didnt took the alternator out of the car because they said that they could check with one of there tools as long as the car was running. What eals should I check for should I replase the battery again or do I hae to take the alternator out of the car so they could check it better what should I do? If you had these problem with these car or any other what did you do to fix it ill try it, I dont whant to take it to a Auto shop I like to do the work my self.