how do you know it's not the battery? when the car sits for a few days, there is a slow drain on the battery for the ECM, radio memory, etc. when you go to start it, it may click because it doen'st have enough juice to turn the motor, but enough to engage the solenoid. if you are saying the battery is ok based on the radio and other electricals operating, keep in mind that these electricals require low current draw... but your engine requires a large one.
if it clicks after a few days of sitting, how does it finally start? do you jump it? do you keep trying until it finally starts? how does it sound when it does finally start?... strong or weak?
autozone or advance auto can troubleshoot the starting system for free. they check the battery with a load.