Li-Mg dual-salt batteries (DSBs) have attracted growing attention, because a novel way to construct high-energy density DSBs is to take advantage of respective carrier cations. However, previous studies on Li-Mg DSBs have been almost limited to Daniell-type batteries, not attaining rocking-chair-type batteries with high-energy densities. In this work, we show experimentally that concomitant intercalation of Li and Mg ions into the Chevrel compound Mo6S8 in almost equal proportions can occur when discharging in a LiTFSA-Mg(TFSA)2/triglyme(G3) electrolyte. By exploiting this feature, we confirmed with two-electrode coin cells that non-dendritic electrodeposition morphology is available after charge. This work indicates the feasibility of room-temperature rocking-chair-type dual-salt batteries, which provides a new strategy for future safe “metal-anode” rechargeable batteries with high energy densities.