1997 Jeep Grand Cherokee Laredo battery problems/ starting problems

My 1997 jeep grand Cherokee Laredo doesn't start all of the sudden I put the key in all power seems to be on cd lights and what not work. I turn the key and it makes a churning slow type of sound but cant get enough to start. It sits for about two days and I go to my car and its completely dead car key clicker wont work, I have to open the car with key, then I try to turn on and all power is dead..... So next get a buddy to help jump I get it charged off of another battery ( took a good 20min of charging of of his ) then the car finally started. I drive it for awhile then it happens again..

some problems that are wrong with the car are sometimes it will do nothing when I try and start it in park then I put it in neutral and it starts fine but usually it starts in park but every once in awhile it has to be started in neutral.

I am planing to try and test alternator and battery after I get a jump again but what else could it be I have a feeling that they are fine but im not sure at all

If you have ANY INFO on the problem im having id appreciate the help!