This study demonstrates the feasibility of using water and the contents of waste Li-ion batteries for the electrodes in a Li–liquid battery system. Li metal was collected electrochemically from a waste Li-ion battery containing Li-ion source materials from the battery's anode, cathode, and electrolyte, thereby recycling the Li contained in the waste battery at room temperature. The harvested Li metal in the battery system was discharged to produce electricity by using water as the cathode. The discharge voltage of the water showed 2.7 V at 0.1 mA cm−2versus Li metal harvested from waste Li-ion batteries, compared to 2.8 V versus fresh Li metal at the same current rate. Since the electrodes for this proposed battery system are water and the contents of waste Li-ion batteries, the cost of the battery decreases, which is an attractive strategy for a large size energy storage application.