If you have disconnected either of the posts, then it sounds like a dead battery to me.
Sometimes one or more cells will die. The other cells are holding a charge so it seems like it's "ok", but then what happens is the good cells are continuously trying to charge the dead ones.... which is a loosing battle.
Have you checked your battery with a hydrometer?
Here is a good resource to learn about the care and feeding of batteries
The 12volt Side of Life (Part 1)