To find the CG location measure back from the leading edge of the wing. Since you have a 3 1/2" - 4 3/8 " range, start in the middle of that range and mark that spot. If you have a CG Balancing machine you can do the same as in the attached diagram. If you don't, have a friend help you. Turn the plane upside down, each of you place a finger tip at the outside edge of the wing at the CG point, and lift the plane. Before adding weight to the plane to adjust the CG try moving the battery forward or back wards to get the plane to balance on the CG.

Hope this helps

Ken