Purpose: The study aims to understand the effect of the use of fins in the PCM region on the thermal characteristics of the system. This study has two objectives. It is desired to reduce the temperature of the battery and, at the same time, to provide more uniform temperature distribution in the cell, thanks to the appropriate arrangement of the fins. Theory and Methods: The Enthalpy method is employed to solve the energy equation in the PCM region. This region is handled with the assumption of stationary PCM for some analyses. This assumption means that only thermal conduction is taken into consideration. Besides the conduction, natural convection inside the PCM is put into account to understand the importance of the convection inside the PCM. Transient numerical simulations are conducted via ANSYS/Fluent software. The periodic boundary condition is applied, and only a slice of the battery has been modeled to reduce the computational effort. The boundary conditions are presented in Figure A (a) Three different geometry are examined. These are without-fin, 6 -fin and 12-fin cases. The analyses have been carried out for 1.43 W and 2.75W heat generations corresponding to the lithium-ion discharge rates of 2C and 3C. PCM types, CrodaTherm29, Paraffin-wax, and RT35 are examined in the study. Results: Natural convection effect should be considered, especially for 12-fins geometry, as the battery temperature at 6000 s (1.43 W heat generation) difference between two models is found as 7.9 K (2.5% difference). For the 2.75 W heat generation case, 6 and 12 fin geometries have reduced the average battery temperature 9.4 K (2.6%) and 15.18 K (4.2%), respectively at 6000th s. The use of fins not only reduces the average battery temperature but also provides more homogenous battery temperature. Simulations performed for 1.43 W heat generation show that the temperature difference between the lower and upper surfaces of the battery at the end of 5000th s are 5.9 degrees C, 3.2 degrees C, and 1.9 degrees C for without fin, 6 fin, and 12 fin cases, respectively. Figure A (a) shows by using 12 fins for 1.43 W heat generation, all PCMs have successfully kept the battery temperature below the critical value of 50 degrees C for 7000 s period. Conclusion: Present study proves that the use of fins is very effective in terms of ensuring cooler and more uniform temperature distribution in the cell. Putting into account the convection effects in PCM is a must if the fins are present in the system.