battery troubles

[lx mike]

Well at work i moved my car around abck so i wouldn't have to walk so far to the parking garage and when i went to go home all i got was a "click" and then nothing. i check the terminals and they are tight. I got a boost from mt friend and when we took the cable off my battery the lights would dim and engine would surge and then die. we tried again and left them on a bit longer before jumping and got same thing. the second time we did it i watched the ammeter and it would go down to almost the bottom and jump back up when surging, It did take a while to start. when we first tried it turned over slowly and we let it sit a minute then tried and it started. second time we let it sit and it turned over just enough to start but not as quick as it usualy does. is it my battery or maybe the cables or soemthing else i can check??