Flexible energy storage devices are at the forefront of next‐generation power supplies, one of the most important components of which is the gel electrolyte. However, shortcomings exist, more or less, for all the currently developed hydrogel electrolytes. Herein, a facile and cost‐effective method is developed to construct an all‐round hydrogel electrolyte by using cotton as the raw material, tetraethyl orthosilicate as the crosslinker, and glycerol as the antifreezing agent. The obtained hydrogel electrolyte has high ionic conductivity, excellent mechanical properties (e.g., high tensile strength and elasticity), ultralow freezing point, good self‐healing ability, high adhesion, and good heat‐resistance ability. Remarkably, this hydrogel electrolyte can provide a record‐breaking high ionic conductivity of 19.4 mS cm−1 at −40 °C compared with previously reported aqueous electrolytes for zinc‐ion batteries. In addition, this hydrogel electrolyte can significantly inhibit zinc dendritic growth and parasitic side reactions from −40 to 60 °C. With this hydrogel electrolyte, a flexible quasi‐solid‐state Zn–MnO2 battery is assembled, which shows remarkable energy densities from −40 to 60 °C. The battery also exhibits outstanding cycling durability and has high endurance under various harsh conditions. This work opens new opportunities for the development of hydrogel electrolytes. A hydrogel electrolyte with high ionic conductivity, ultralow freezing point, excellent mechanical properties, good self‐healing ability, high adhesion, and good heat‐resistance ability is constructed. It can effectively suppress the growth of zinc dendrites and the occurrence of parasitic side reactions, thereby enabling a high‐performance flexible quasi‐solid‐state Zn–MnO2 battery that can work normally in a wide temperature range.