A battery thermal management system (BTMS) aims to control battery temperature and maintain thermal uniformity in a battery module to avoid thermal degradation of the battery and thermal runaway. Hence, it is indispensable for an electric vehicle's safe and efficient operation. The present study proposes a novel variable contact area relationship for designing a liquid-cooled BTMS. The contact area between the battery and the coolant is increased along the flow direction to ensure almost identical heat removal from each battery to maintain a uniform temperature across the battery module at extreme operating conditions. A battery module containing twenty-four 18650 Lithium-ion batteries is considered. The heat generated in the batteries is removed using the coolant (water). A three-dimensional computational fluid dynamics (CFD) model of the battery module is developed and validated. Multiple geometric iterations are performed using the proposed relationship to obtain the contact area between each battery and aluminum block. The ensuing variable contact area geometry achieves significant reductions of 73.9 % and 72.5 % in the maximum temperature difference ∆Tmax of the battery module compared to the constant contact area geometries. Furthermore, a significant reduction in the maximum temperature (Tmax) within the battery module is also observed. The variable contact area geometry is 57.2 % lighter than the maximum constant contact area geometry and performs significantly better. The influence of the coolant flow rate, the contact angle between the battery and aluminum block, and the heat generation rate of the battery on Tmax and ∆Tmax are also explored.