Your energy can only be restored up to the maximum. If the energy-regeneration timer stops—typically when using a talisman or artifact—that means that your energy has reached the maximum or that you used a talisman when your energy was full. The talisman will start working once your energy drops below the maximum.

However, keep in mind that the talisman has its own timer that will continue to count down even when the talisman is idle, so it's best to use talismans and artifacts only when you have little energy.