From time to time you may have an opportunity to watch a video to get a "Rapid Recharge" boost.
The Rapid Recharge boost does not increase your energy. Rather, when your energy level falls to 5 or below, it reduces the cool-down at which your energy regenerates. The effect of this boost lasts about an hour, for each time it is triggered.
You may not notice this effect visibly in the cooldown timer unless your energy has gotten fairly low - around 5 or so - but it is still in effect whatever your energy level is.