Seawater activated batteries based on Mg and Ni/Al electrodes were constructed and investigated at different electrolyte temperatures. The Ni/Al coatings which were applied as the cathodes for seawater activated batteries were produced by plasma spray deposition. Voltage-time (U=E-IR(t)) dependence was measured for the galvanic pair Mg-Ni/Al, where I was constant current, E the electromotive force of the galvanic pair and R(t) the variable resistance. It was found that U(t) inclination depends on the anode corrosion rate, and the mass of the anode is the only parameter that restricts the life time of the seawater activated cell. The current density of this cell was found to be a linear function of the temperature of the seawater. Output power density dependence on the spacing between electrodes and number of cells was investigated for cells with different electrode area. A maximum output power density of 3 x 10(4) W/m(3) was obtained for these cells.