Safe and efficient operation of lithium-ion batteries in electric vehicles (EVs) relies on the performance of the thermal management system. For optimum thermal management, precise estimation of heat generation rate is crucial. This paper illustrates the criticality of the inclusion of explicit in-situ temperature dependence of heat generation rate as opposed to the state of the art models. We test a cylindrical LiFePO4 (LFP) cell over a broad range (typical of EV cells) of discharge rate (2.3 C-13.6 C) and temperature (20 degrees C-70 degrees C) and observe a non-monotonic trend where heat rate decreases first up to 55 degrees C to 60 degrees C (depending upon the discharge rate) and then starts to increase. The trend does not fit into any existing heat generation model of Li-ion battery, and hence we separately include it to simulate the heat transfer behaviour of a module. Simulations confirm the substantial difference of temperature from the conventional analysis where the temperature dependency is characterized inadequately. Current work demonstrates the counter-intuitive non-monotonic temperature dependence of heat rate, the effect of the same on peak module temperature and thus assists in improving the design methodology of the thermal management system of EV battery packs. Highlights Dynamic correlation between temperature and heat generation is measured experimentally. Cylindrical Li-ion cells are tested for typical electric vehicle operation ranges (2.3 C-13.6 C and 20 degrees C-70 degrees C). Counter-intuitive decreasing-first-increasing-later trend is observed for all discharge rates. Temperature dependence of in-situ heat rate is explained and included in analysis. Major modification is observed for the peak cell temperature, a critical design parameter.