The initial state of the battery developed by Yi Cui, with two electrodes immersed in fresh water. Purple and orange dots represent positively and negatively charged ions, respectively. In Step 1, a small electric current is applied to charge the battery, pulling ions out of the electrodes and into the water. Step 2, the fresh water is purged and replaced with seawater. Note much higher abundance of charged ions in the salt water. Step 3, electricity is drawn from the battery for use, draining the battery of its stored energy. Ions return to electrodes. Step 4, seawater is discharged and replaced with river water, for the cycle to begin anew.