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Summary Easy regenerability of core components such as electrode and electrolyte is highly required in advanced electrochemical devices. This work reports a reliable, regenerable, and stretchable hydrogel electrolyte based on ionic bonds between polyacrylic acid (PAA) and polyallylamine (PAH). PAA-PAH electrolyte (1M LiCl addition) exhibits high ionic conductivity (0.050 S·cm-1) and excellent mechanical property (fracture strain of 1,688%). Notably, the electrolyte can be regenerated to any desired shape under mild conditions and remains 96% and 90% of the initial ionic conductivity after the first and second regeneration, respectively. PAA-PAH/LiCl-based supercapacitor exhibits nearly 100% capacitance retention upon rolling, stretching, and 5,000 charge-discharge cycles, whereas the regenerated device holds 97.6% capacitance of the initial device and 90.9% after 5,000 cycles. This low-cost, high-efficiency, and regenerable hydrogel electrolyte reveals very promising use in solid-state/flexible supercapacitors and possibly becomes a standard commercial hydrogel electrolyte for sustainable electrochemical energy devices., Graphical Abstract, Highlights • Highly reliable PAA-PAH/LiCl electrolyte for flexible supercapacitor is developed • PAA-PAH/LiCl hydrogel electrolyte can be easily regenerated under mild conditions • Regenerated hydrogel shows high retention of ionic conductivity and extensibility • Regenerated device reserves >90% capacitance and durability of the original one, Energy Materials; Materials Science; Polymer Chemistry