Were you on full hp when you tried and do you literally mean 70 times?
Yes,I try it 70 times in Viridian Gym 2. I just bring one pokemon to fight with Giovanni. It like a gambling. If i can save 1 HP under his hand, it will be easy to win. In fact, every time I fight, I just can see my pokemon die after 1 move. Is Focus Band do not work when hit by super effect?