The paper aims to study the time required for the Li-ion battery to dissipate/heat under the high/low temperature conditions of electric vehicles, and improve the insulation and safety design of the battery thermal management system (BTMS). The dynamic characteristics of the heat dissipation process of the Li–ion battery cells applied by the microchannel coupled micro heat pipe (MC-UMHP) BTMS are analyzed through transient simulation, and the electric heating auxiliary design is added to the BTMS structure. Taking into account the Li–ion battery cells under various unfavorable conditions during ultra-low/high temperature operation, heat preservation and safety design are added to MC-UMHP type BTMS. The results suggest that when the flow rate is 3 m/s, the time required for the MC-UMHP type BTMS to cool the Li–ion battery cells from the initial temperature of 314 K to the target temperature of 303 K is only 135 s. When the initial temperature is 258 K, the heating time is approximately 258 s. The maximum temperature difference of the Li–ion battery cells in the dispersion/heating simulation experiment under various working conditions is always less than 5 K. The MC-UMHP type BTMS requires less time to dissipate/heat the Li–ion battery, with good heat exchange effect and good temperature uniform.