Battery//Electric Issue

2002 Hyundai Elantra 5dr

I had to replace the battery and when I did all of a sudden the stereo and headlights stopped working, figured it was a ground issue or fuse but would fix it later, took the battery out, when I put it in and let the car run for awhile the battery died. Tried it in another vehicle and was dead. The altenator was replaced last year, so I dont believe it the issue, but I am not really a car person so I have no clue. Any help?