Provided is a method for increasing the rate of recovery of valuable metals when waste batteries batteries are treated by a dry process. The valuable metal recovery method in the dry step S20 includes a melting step ST21 including melting waste batteries to form a melt, a slag separation step ST22 including separating slag from the melt, and an alloy separation step ST23 including separating an alloy of valuable metals from the melt, wherein the slag has an aluminium oxide content of 20% by weight to less than 75% by weight and an iron content of 5% by weight to 40% by weight, calculated as metallic iron, and silicon oxide and calcium oxide are added as fluxes in the melting step ST21 so that the slag can have a melting point of at least 1,500° C., preferably at most 1,650° C.