The accelerated demand for electrifying the transportation sector, coupled with the continuous improvement of rechargeable batteries’ characteristics, have made modern high-energy Lithium-ion (Li-ion) batteries the standard choice for hybrid and electric vehicles (EVs). Consequently, Li-ion batteries’ electrochemical and thermal characteristics are very important topics, putting them at the forefront of the research. Along with the electrical performance of Li-ion battery cells, their thermal behavior needs to be accurately predicted during operation and over the lifespan of the application as well, since the thermal management of the battery is crucial for the safety of the EV driver. Moreover, the thermal management system can significantly lower the degradation rate of the battery pack and thus reduce costs. In this paper, the thermal characterization of a commercially available Nickel-Manganese-Cobalt (NMC) based Li-ion battery cell was performed under different operating conditions: state-of-charge (SOC) levels, charge/discharge current rates and operating temperatures. Moreover, by carrying out accelerated cycle ageing tests on a total of nine NMC-based Li-ion battery cells, the effect of ageing on the most important thermal parameters was investigated.