What do you think could be going out. Starter, Starter Solenoid, or bad battery?

I have a 2006 chevy tahoe, and I was told by the dealer that i need to look into getting a new battery (which not I plan on getting this friday). When I try to crank the tahoe, it clicks, and nothing else, however when i connect the jumper cables to another vehicle it cranks normally. Also, how do you know if your a/c is over charged?