This article addresses lithium-ion battery performance degradation in extreme cold environments, which causes charging inefficiency or failure in portable power banks, by designing a multi-modal cooperative charging system. Low-temperature electrochemical mechanisms and charging behavior are investigated, focusing on coupled electro-thermal relationships. Optimized preheating structures and electro-thermal cooperative dynamic charging strategies are proposed. A polyimide-based flexible heating film integrated with high-thermal-conductivity AlN/graphene significantly improves heat transfer rate and uniformity, rapidly restoring charging capability. To overcome limitations in direct internal temperature measurement, the recursive least squares method with a forgetting factor enables online identification of drifting key parameters (e.g., thermal capacity, resistance). A high-precision, time-varying thermal circuit model is formulated. Combined with an unscented Kalman filter, a dual closed-loop cooperative estimation architecture recursively updates and corrects internal temperature states in real-time. Experimental validation confirms the system achieves a battery internal heating rate of 5℃/min. The thermal model's systematic error stabilizes within 0.2℃. Under various sub-zero conditions (-30℃, -20℃, and -10℃), internal temperature prediction errors remain within ±1℃, with a maximum absolute error of 0.6℃ and maximum root mean square error of 0.4℃. This effectively solves the critical issue of portable power bank charging failure in extreme cold, providing innovative theoretical and engineering foundations for energy assurance systems in such environments.