Battery dead

I replaced the battery and it starts up fine if driven every day, but when left setting for a few days to a week the battery seems to be dead. Then today I started it drove about twenty miles and shut it off had my hazard lights on for about fifteen minutes waiting for a friend to meet went to start it up and would not start I had to call my son for a jump and keep in mind this is a handi capped accessable vehicle if that matters. Thank you