A power source, designed to be bent or flexed during use, may include a layer of anode material having a length greater than a layer of cathode material to accommodate for movement of the cathode or anode layers during flexing of the power source. An enclosure containing the cathode and anode materials may include an inner protective layer proximate to the cathode and anode layers and a water-impermeable layer external to the inner protective layer. The water-impermeable layer may have a pleated or corrugated configuration that may be extended when the power source is bent under application of a flexure stress, preventing damage or deformation to the water-impermeable layer.