You didnt need to totally remove the nut, just loosen it. Just rotate the clamp side to side and it should loosen up enough to pull off. There should be a vent hose attached to one side of the battery, be carefull not to break it when removing it. It should pull straight out from the side. Then remove the battery clamp. To install the cable back on just push them on the battery posts as far as you can and tighten the nuts on the cable ends.