A solid state battery includes a flexible polymer sheet, and an array of solid state pillars supported by and extending through the sheet. Each of the pillars has an anode layer, a cathode layer adjacent, and an inorganic solid electrolyte (ISE) layer interposed between the anode and cathode layers. A flexible electrochemical membrane includes a flexible polymer sheet, and an array of inorganic solid electrolyte pillars supported by the polymer sheet with each of the pillars extending through a thickness of the sheet to form an ionically conductive pathway therethrough.