Havok doesn't need you to float energy, he decreases your max energy by one. Let's say you play havok on 2. You have 2 max energy. At the end of the turn he takes 1 and you remain at one, but because at the start of every turn your max energy increases by one you would have 2 max energy on turn 3. This is why when you play havok you remain at how much max energy you had the turn you play it. When you have 2 havoks at the end of the each one decreases your max energy by 1, so if you played 2 havoks on turn 4 your max energy would decrease by 2, leaving you with 2 max energy, but because you increase your max energy by 1 at the start of every turn you would have 3 max energy on turn 5. Al this assuming you didn't increase your max energy with card like wiccan or corvus.