J.N.
You mention he is very strong willed, and wonder how to win a battle of wills. My son is also like this (strong willed, especially on the potty issue). I completely refuse to fight with him. I just let him go (whether this means run naked or go back to baby diapers). When he wanted to do something fun, especially nintendo, I calmly told him that it was something for big boys, and that big boys go in the potty. No fight, just a matter of fact statement. It was always something he wanted NOW, becuase school is just too far off for him to make a difference. I refused to fight, argue, or yell, but would not give in. It took a few months, but once he saw that I wouldn't fight and I wouldn't back down, he was 100% trained in a week. Good luck