Heat generation behaviors during charge and discharge are examined by calorimetric measurement for several lithium-ion cells that are commercially available. Heat flow from the cell shows interesting variation reflecting the characteristics of the electrode reactions. Heat generation of the cell with graphitic carbon anode draws extremely complicated curve caused by variation of stage structure of Lithium intercalated graphite. The cell with hard carbon anode dissipates excess heat resulting in a voltage hysteresis between charge and discharge. In the LiCoO2 cathode, thermal behaviors due to the crystal phase transition are clearly observed.