During cycling, the temperature of a Li-Ion cell changes as a result of reversible and irreversible aspects of the internal electrochemistry, as well as concentration gradient dynamics. A method for real-time estimation of any of these components of heat generation is presented. Experiments are performed to quantify the reversible component of heat generation across a broad range of state-of-charge values for an automotive cell. The state-of-charge dependency of the reversible heat is fit using half-cell data from literature. A lumped energy balance model is validated with cycling data to demonstrate the range of applicability for the process, and a Kalman Filter is designed to utilize the energy balance for estimation of reversible heat generation from cycling data. The estimates are compared to the values obtained from experiments for multiple current rates and temperatures, and key advantages of the model-based method are discussed.