With reference to FIGS. 2 and 3, a leaktight, thin wall housing 60 for the electrode plate stack (electrode plates and separators) is fabricated from two thin sheets 61 and 62 of a flexible polymeric material such as polyethylene, fluorinated ethylene propylene, polyethylene terephthalate, or other similar materials, or combinations thereof, which have a low oxygen and water vapor permeability cha