An experimental method was created for assessment of the efficiency of the closed oxygen cycle in VRLA cells. It was experimentally established that at 25% compression of the AGM separator the battery life is the longest one. On the other hand. the efficiency of the closed oxygen cycle (COC) is the highest at 20% compression of the AGM. With an increase of the compression the efficiency of the COC decreases because of the decreasing of the number of the channels (pores) along which the oxygen flows can move through the AGM separator. It was established that the polarization of the VRLA cell is mainly determined by the resistance arising at transportation of the oxygen through the AGR I. There is an upper limit of the rate of recombination of oxygen that depends on the structure and properties of the AGM. With increase of the temperature the efficiency of the COC and polarization of the VRLA cell decrease. During cycling, the properties and structure of the AGM change that affects the parameters of VRLAB. (C) 2000 Elsevier Science S.A. All rights reserved.