The demand for energy storage systems has been steadily increasing, and aqueous rechargeable metal-ion batteries (ARMBs) have emerged as promising next-generation technology due to their superior safety, environmental friendliness, and economic feasibility. Despite these advantages, the inherent limitations of aqueous electrolytes, including parasitic gas evolution arising from the narrow electrochemical stability window, dynamic pH fluctuations, temperature-dependent ionic conductivity, and dendrite growth, remain major obstacles to practical implementation. Among these, thermal instability is a fundamental technological hurdle to commercialization. This review examines the degradation mechanisms of ARMBs under extreme temperatures, outlines polymer electrolyte design strategies for stable operation, and proposes future research directions to enable their application in extreme environments and grid-scale systems. Overall, improving thermal stability is expected to accelerate the adoption of ARMBs.