Praying is being-in-relationship-with God, rather than some religious duty that one has to do.
I communicate with Linda, not because I "have to," but because I love her. To only talk and listen to her out of duty would be a sign of a strange, unsatisfying marriage.
Philip Yancey writes: "Prayer as transaction rather than relationship can decline into a practice more duty than joy, an occasional and awkward exercise with little connection to life." (Yancey, Prayer, Kindle Locations 844-845)
How I communicate with Linda when no one else is around is an indicator of how I view her and our marriage. In a similar way how I pray shows how I view God. "Who one believes God to be is most accurately revealed not in any credo but in the way one speaks to God when no one else is listening." (Nancy Mairs, quoted in Ib., Kindle Locations 820-822)
To pray is to be in relationship with God. Prayer is not something we have to do. When you are in a real, loving relationship you communicate.