In this paper, a sodium ion selective electrode (Na-ISE) and a bromide ion selective electrode (Br-ISE) were used to form a liquid-free potential reversible battery: Na-ISE vertical bar NaBr (m(1)) and SrBr2 (m(2))vertical bar Br-ISE. The mean ionic activity coefficients of NaBr in the ternary system NaBr-SrBr2-H2O at 288.15 K were determined using the cell potential method. 0.8 In this system, the total ionic strength, I, ranges from 0.0100 up to 2.0000 mol.kg(-1) for different ionic strength fractions of y(b) SrBr2, that is, y(b )= (0.0, 0.2, 0.4, 0.6, and 0.8). The results show that Na-ISE and Br-ISE have a great Nernst effect. The mean ionic activity coefficients of NaBr in NaBr-SrBr2-H2O were calculated using the Nernst equation, and the cell potential values were measured. The Pitzer ion interaction parameters theta(Na+ center dot Sr2+) and Psi(Na+ center dot Sr2+ center dot Br-) were fitted using the Pitzer model, and experimental results in this work, and the mean ionic activity coefficients of SrBr2 at 288.15 K were also calculated according to the Pitzer model. Finally, the osmotic coefficient Phi water activity a(w), and excess Gibbs energy G(E) of the ternary system were also calculated.