The ornamental design for a portion of a charging apparatus, as shown and described.
FIG. 1 is a front top perspective view of a charging apparatus showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a right side view thereof; and,
FIG. 4 is a top view thereof.
The portions of the images shown with broken lines are for illustrative purposes only and form no part of the claimed design. The shade lines in the figures indicate a character or contour of the claimed design, and do not depict any particular color, texture, or material.