Realize that there is only one willpower and everything including all your actions are governed by this willpower. Surrender more and more to this willpower and learn to live your life from there. At the root of it your will and this will are one. At the more surface level you believe you are separate from this, and struggle against yourself. As we realize our oneness with this willpower, the struggle patterns (struggle and depletion, struggle and depletion) are replaced with a flow type of experience, where everything flows more and more naturally as we progress.
The most efficient way to replenish willpower is to awaken from the illusion that you have a separate willpower. Only illusion needs maintenance and replenishment. Truth stands for itself without needing any support.