can't seem to remove + connection on battery

Just bought a used 96 Cavalier now it won't start.
I want to replace the battery and I've done this lots before but I think this must be my first side mount.
I unscrewed the - and + bolts from the side and the negative cable came off no problem.
I've removed the cables attached except the + terminal and I can't get it off the side of the battery.
So here are my options as I see them:
- it's very cold here so I don't know if it is just frozen on (seems unlikely)
- the post was corroded so maybe it's sort of stuck now
- there is a larger post? that the smaller bolt screwed into that maybe needs to be removed to get it off (hard to explain but it seems like about an 18mm sized post that extends through the red connector). I tried to turn with a crescent wrench since I don't have an 18mm wrench or socket) but I don't get enough torque on it (slips).
Any tips? I have a picture if I can post it somehow.
I guess I could always cut the connector and re-connect with a new one but it seems kind of extreme.

 

Just go to the autostore and get a 3/8 or 1/4 ratchet with the socket....should cost you under $10.

 

either socket if room or wrench if not to remove, then clean between the bolt and the cable as well as between the cable and the battery, be carefull when reasembling not to over tighten and strip out the battery.

Murphy was an optimist

 

Will do, just wanted to get some confirmation/clarification before I went about it the wrong way.

 

11/16th did the trick. I think it is was an extra post added for the command start and stereo.