A sealed lead-acid battery of the absorption-at-the-negative-electrode type employing an immobilized liquid electrolyte in which stratification of the electrolyte is eliminated. In accordance with the invention, a lower part of the positive and negative plates is supplied with water formed by a reaction or phase change of substances contained within the container of the battery. In a preferred embodiment, this is done by producing a temperature difference within the container. Also, water may be provided to the lower part of the positive and negative plates by increasing the speed of certain reactions at the lower part of the negative plate relative to the upper part thereof.