If my energy bar is full can I purchase an extended energy bar to double the energy for competition?

Sorry, I misread the original poster's question about the extended energy bar, which will add one- time only, 450 energy to what you already have (4x your energy, which you can use for competition). After you deplete that energy, your energy will refill to 150 (instead of 110) at the same rate, which takes 10 hrs. After you buy it, star boosters and character puzzles give 150 energy, instead of 110.