2001 Hyundai Elantra Battery cable stuck?

I have been trying to remove the positive battery cable. It is different than normal cable connecters I am used to. It has a cup shaped head that fits down over the terminal and has a bolt sticking out of the top on which you loosen a nut. This is the only means I can see of loosening the head to remove it from the terminal but I have actually removed the nut and tapped and pryed and done everything I can think of to loosen the head and it still won't come off. I also tryed the baking soda/water solution to break down corrosion. Either it is so badly corroded that it is stuck on or I am doing something wrong in trying to loosen the head to remove it. I feel like I'm going to break the terminal right out of the battery if I pry any harder. Any ideas or experienced advice from anyone else who has used this type of cable would be appreciated.