Could be battery, or your starter motor could be getting tired, or you could have a connection somewhere getting corroded or something. Whatever you do, don't get a delco battery, their battery terminals are famous for breaking off and leaking acid (mine did it, so did my dads). I got an Optima red top last may and couldn't be happier. Other good batteries are die hard and exide. There are very few batteries I would get form Pep Boys or Autozone, although I got my optima at autozone...