car dies then comes alive later

[HiImBrian]

This has happened before in the near past. So I replaced the battery and went back to school. A week later I came home and it was dead again. So I went and got it replaced once again. So I don't think it's the battery, I think there is something causing the battery to die, considering this one is less than a month old. I don't have subs or anything that I can think of that would be drawing power. The cables aren't corroded, I replaced those with the battery the first time. And obviously the terminals aren't corroded either. I'll check the connection again, but I'm pretty dang sure they are on there good. I put a little Vaseline around the terminals before I put the cables on. I heard that helped with corrosion a little, could that be my problem?