<p>An effective lithium-ion battery thermal management system (BTMS) ensures the safety of electric vehicles (EVs) and energy storage systems. Immersion cooling is known for high efficiency and excellent temperature uniformity. To address the high energy consumption of secondary cooling loops in vehicles for cooling immersion oil, this paper proposes a method of immersion coupled cooling tubes. Battery heat is directly absorbed by the immersion liquid and rapidly dissipated via cooling water in the S-type cooling tube (SCT). This work investigated the effects of structural parameters, immersion fluid medium, and operating parameters on the cooling performance of the BTMS. The results showed that the fin height (<i>h</i>_f) has no significant effect on the cooling performance. Both Transformer Oil and HFE-7100 delivered outstanding thermal management, reaching a maximum of 36.73°C and 41.39°C while maintaining narrow temperature differences of only 3.70°C and 2.09°C apart, respectively. When the ambient temperature reached 40°C and HFE-7100 was used as the immersion liquid, the maximum temperature difference remained consistently below 3°C. Subsequently, a sensitivity analysis was conducted on the respective influential parameters. It was found that inlet water temperature (<i>T</i>_in) and immersion fluids exert the most significant influence on the system performance. Finally, different immersion cooling schemes were compared, which demonstrated the advantages of the system proposed in this study under harsh condition, thereby supporting the application of different schemes under various scenarios. It can be directly integrated with the vehicle-mounted cooling circuit system, thereby reducing energy consumption and weight, and offering new insights for research on thermal management systems for EVs.</p>