Practical modeling and operation optimization of dual-battery portable energy storage systems for low temperatures

In cold regions, low temperatures and heavy snowfall often result in power outages. Portable energy storage systems (PESS) are in high demand in these areas to mitigate the adverse effects of power cuts. However, the efficiency of batteries deteriorates, and their capacity fades substantially at low temperatures. Existing off-grid battery thermal management methods are based on the use of a single type of battery, which may fail at extremely low temperatures (–30 ${}^{\circ }$C) due to battery limitations. Hence, in this study, a dual-battery PESS for low temperatures (PESSLT) is designed to address this issue, and a prototype is manufactured. The proposed PESSLT combines battery thermal management methods with hybrid energy storage methods to achieve a high charge–discharge efficiency and low capacity fading at extremely low temperatures. To achieve accurate energy management of PESSLT, a novel convex battery model considering temperature and power effects on battery charge–discharge efficiency is developed. Additionally, a comprehensive operational model of a dual-battery PESSLT that considers multiple domain constraints is formulated. Simulations based on real data show that at −30 ${}^{\circ }$C, commonly used LFP batteries with heaters can only achieve an average charge–discharge efficiency of 39 %. In addition, this approach suffers from four major drawbacks: unstable startup, rapid capacity degradation, safety risks, and lack of immediate usability. The proposed dual-battery PESSLT, despite a 24 % increase in weight and a 72 % increase in initial investment, achieves an average charge–discharge efficiency of 67 %, addressing all four issues and significantly extending the service life.