During charge and discharge of the lead-acid cell equal amounts ofH2SO4 participate inthe reactions at the
two types of plates (electrodes). However, the charge and discharge reactions at the positive plates involve
also 2 mol of water per every mole of reacted PbO2. Consequently, a concentration difference appears in
the electrolyte between the two electrodes (horizontal stratification), which affects the reversibility of the
processes at the two electrodes and thus the cycle life of the battery. The present paper proposes the use
of a three-layered absorptive glass mat (AGM) separator, the middle layer playing the role of a membrane
that divides (separates) the anodic and cathodic electrolyte spaces, and controls the exchange rates of
H2SO4, H+ ions, O2 and H2O flows between the two electrode spaces. To be able to perform this membrane
function, the thinner middle AGMlayer (0.2mm) is processed with an appropriate polymeric emulsion to
acquire balanced hydrophobic/hydrophilic properties, which sustain constantH2SO4 concentration in the
two electrode spaces during cycling. Three types of polymeric emulsions have been used for treatment
of the membrane: (a) polyvinylpyrollidonestyrene (MPVS), (b) polyvinylpyrrolidone “Luviskol” (MPVP),
or (c) polytetrafluorethylene modified with Luviskol (MMAGM). It is established experimentally that the
MMAGMmembrane maintains equal acid concentration in the anodic and cathodic spaces (no horizontal
stratification) during battery cycling and hence ensures longer cycle life performance