For　practical　applications　in　the　fields　of　aerospace　and　robotic　engineering,　flexible　energy　storage　devices　must　be　stable　under　environmental　temperatures　and　different　deformed　situations.　In　this　work,　a　mechanically　stable　supercapacitor　(SC)　at　harsh　ambient　temperatures　is　synthesized　by　in　situ　polymerization　of　polyaniline(PANI)　onto　a　double　network　hydrogel　electrolyte　from　cross-linked　polyvinyl　alcohol(PVA)　and　polyacrylamide/acrylic　acid　(PAM/AA)　networks.　The　highly　integrated　structure　endows　the　supercapacitor　with　unprecedented　mechanical　performance.　The　devices　can　endure　608%　tensile　strain　and　be　stretched　up　to　50%　without　noticeable　hysteresis,　demonstrating　fatigue　and　fracture　resistance　under　thousands　of　cyclic　loads.　Benefiting　from　an　all-flexible　configuration　through　seamless　integration　of　the　PANI　electrode,　the　supercapacitor　presents　a　high　specific　capacitance　of　95.8 mF cm–2.　It　can　also　work　as　an　all-flexible　device　and　maintain　its　stable　output　under　complex　deformations,　even　physical　damages.　Furthermore,　the　device　delivers　excellent　environmental　adaptability　by　steady　electrochemical　performance　after　operating　at　extreme　temperatures　from　−60　to　100 °C.　Such　a　versatile　supercapacitor　presents　a　potential　application　in　integrated　flexible　electronic　systems　by　powering　functional　devices　in　harsh　environments.　©　2022　Wiley-VCH　GmbH.