Questions about the car battery in my seabring, and charging it.?

Ok, so I'm not sure if the battery is dead. The headlights, and the dash board light up. When i disconnected the battery, there was a second lug nut that i removed right next to the main lug. I think it was for excesseries like the radio. However I dont know how to reconnect the second lug nut, because I think the screw fell out, and you cant get to the battery without taking off the wheel. Also, I need to know if a battery charger would be the same as buying a new battery? I have a charger, but is there an instance where the battery could still be bad even if you charge it? I tried jumping it, but no. and I put a new starter in.