Have you stumbled on The Power of Full Engagement by Jim Loehr[1][2]? It crystallises this idea well, divides energy into several different dimensions and tries to give you a framework to figure out which dimension is constraining you and how to expand your reservoir. Some of the practical advice is silly but I still find it very helpful. I go back to it often.

[1] https://hbr.org/2007/10/manage-your-energy-not-your-time [2] https://www.goodreads.com/book/show/68985.The_Power_of_Full_...