Solid-state aqueous energy conversion and storage are regarded as one of the most promising energy technologies for low-cost and large-scale applications without safety risk. However, current solid-state aqueous batteries can only sustain tens to hundreds of charging–discharging cycles and deliver limited capacities, particularly in alkaline electrolytes. This has severely limited solid-state energy technologies for large-scale applications. Herein, it is reported that a sodium polyacrylate hydrogel electrolyte ensures an order of magnitude higher cycling stability than those of their state-of-the-art counterparts and high capacities for the solid-state Zn//NiCo and Zn–air batteries. The observed superb cell performance is attributed to a high ionic conductivity and water-retaining capability intrinsically associated with the sodium polyacrylate hydrogel electrolyte, coupled with the acrylate-ion-facilitated formation of quasi-solid electrolyte interface to eliminate zinc dendrites.