Research on the thermal behavior of Li-ion batteries fosters the understanding of heat generating effects and the dimensioning of battery thermal management systems (TMS). First comprehensive studies with a new DSC-like calorimeter for coin-cells are performed to determine thermal properties of a LiCoO2-graphite cell. The high precision and accuracy of the measurements are obtained by calibrating the signals using melting point standards in properly prepared coin-cell cases. The heat flow is measured during cycling with different C-rates between 0.23 C and 0.9 C under isothermal conditions at temperatures between 30 °C and 50 °C in steps of 5 K. Chemical and physical changes are identified in the measured heat flow signal and are discussed taking into account phase diagram information. Energetic efficiencies are calculated in dependence of temperature and C-rates by integrating the measured electrical power and heat values. The influence of cell aging on heat generation and usable capacity under operating conditions is shown. Considering the measured heat generation in a wide temperature range at different C-rates will make a valuable contribution to the understanding of material properties. This fundamental data is essential to improve thermal models to simulate spatially resolved heat dissipation in the electrodes to prevent over-heating.