The paper discloses the influence of the temperature and electrolyte saturation of the active block (positive and negative plates and AGM separator) on the rate and efficiency of the oxygen cycle (OC) in valve-regulated lead-acid batteries (VRLAB). Applying steady-state cyclic linear sweep voltammetry and measuring the gas flow leaving the cell, the rate and efficiency of OC were measured at constant temperature and electrolyte saturation as a function of the negative plate potential. The obtained results show that at constant potential of the negative plate the rate of the OC depends slightly on temperature. However, the efficiency of the OC strongly depends on the temperature-the higher the temperature, the lower the OC efficiency. The experimental results for the influence of the electrolyte saturation on the rate and efficiency of the oxygen cycle show that the saturation is the main rate- and efficiency-limiting factor. Combining the gas diffusion approach, porosimetric analysis of the NAM and AGM separator and the recently proposed model of the reactions that take place during the operation of OC, the mechanism of the influence of the electrolyte saturation on the rate and efficiency of the oxygen cycle was elucidated. It was shown that the optimal saturation value is about 93%. (c) 2005 Elsevier B.V. All rights reserved.