The changes in H2SO4 concentration in the anodic and cathodic
spaces were measured with the help of a refractometer after the
end of charge and discharge of the cells with three-layered separators
employing a method developed earlier [1]. Samples of the
electrolyte were taken from nine different positions of the 2.4mm
AGM separator forming the anodic space and of the 1.8mm separator
forming the cathodic space, namely: from three horizontal
and three vertical zones along the height of the plates. The obtained
results were averaged to three H2SO4 concentration values corresponding
to the three horizontal zones along the cell height.