Great but why are you wasting Voldemort’s magic core and not using it to help increase your own by when your reserves are out use his and since and repeat?
Because our Mc is stubborn and compares himself to geniuses like Dumbledore, Grindelwald and Voldemort.
He wants to know how much power can be achieved with his effort rather than taking the simple way.
The secondary reserve has a purpose which will be revealed later in the story.