A flexible secondary battery includes an electrode assembly having a first electrode plate, a second electrode plate, and a separator between the first and second electrode plates; and a pouch comprising a plurality of outwardly extending protrusions, the pouch sealing the electrode assembly and an electrolyte therein, wherein the pouch is configured such that a degree of strain of the electrode assembly resulting from bending of the pouch is lower than a degree of strain on the pouch from formation of the protrusions.