Batteries are one of the main tools to provide the flexibility distribution and transmission systems need due to their increasing dependence on weather conditions. However, environmental and economic factors pose a significant problem. New types of batteries that do not rely on rare earth metals and organic solvents but instead use water and more common ions could be a cost-effective and environmentally safe way to provide energy storage in the future. We studied the performance of sea-salt cells designed as a low-cost, environmentally friendly method to store electricity. We used a constant current charge/discharge test with different currents, from 50 mA to 300 mA, to identify the maximum efficiencies of the cell. Then, we introduced a new strategy to determine the cut-off voltage to discharge the battery, inspired by the maximum power point found in photovoltaics. We used a constant voltage charge to determine the cell’s energy density. However, evidence of side reactions urged us to use constant current charge/discharge tests to identify the battery’s capacity based on the efficiencies drop. Results showed a maximum energy efficiency of 74.6% at 200 mA and a maximum Coulombic efficiency of 88.7% at 300 mA. The cut-off voltage of the cell during discharge should be between 1.4 V and 1.6 V. The energy densities range from 10.1 Wh/kg(6.53 WhL) with an efficiency of 57.5% and 4.18 Wh/kg(2.7 WhL) with an efficiency of 69.8%.@en