The efficiency and effectiveness of a battery thermal management system (BTMS) primarily depend on the limited heat dissipation capacity of the phase change material (PCM). In this study, a novel extended-surface PCM composite is designed to enhance the thermal management of lithium-ion batteries. Numerical investigations using ANSYS Fluent reveal that incorporating metallic fins significantly improves heat transfer by creating a multichannel thermal network. The modified BTMS demonstrates a 92.5% increase in operational duration compared with conventional PCM systems. Additionally, increasing the fin length from 6 to 14 mm improves operational time by 13.62%, while uniform fin placement enhances thermal performance by 9.25%. At higher ambient temperatures (20 degrees C-50 degrees C), the system achieved a 1.96-fold increase in operational duration compared with traditional setups. Furthermore, the optimized BTMS maintained the battery temperature below 60 degrees C for 41%-93% longer durations across varying configurations, outperforming existing systems in high-temperature environments. These findings validate the effectiveness of extended-surface PCM composites in overcoming the limitations of conventional BTMSs, enhancing both battery performance and longevity.