Microcalorimetry has been examined as an efficient method for studying the thermal effects of charge and discharge of Ni-MH batteries. The calorimetric measurements indicate that the net heat dissipation during charging is larger than that during discharging at the same rate. It is observed that the ratio of heat dissipation to charging energy varies with charging capacity, and almost 90% of the charging energy is lost as heat dissipation near the end of the charging process at a rate of 97.7 mA. A jump in the thermal curve near the end of discharge due to a secondary electrode reaction has been observed.