A general form of the thermal energy equation for a battery system is derived based on first principles using the volume-averaging technique. A thermal-electrochemical coupled modeling approach is presented to simultaneously predict battery electrochemical and thermal behaviors. This approach couples the thermal energy equation with the previous multiphase micro-macroscopic electrochemical model via the heat generation and temperature-dependent physicochemical properties. The thermal-electrochemical model is multidimensional and capable of predicting the average cell temperature as well as the temperature distribution inside a cell. Numerical simulations are performed on a Ni-MH battery to demonstrate the significance of thermal-electrochemical coupling and to investigate the effects of thermal environment on battery electrochemical and thermal behaviors under various charging conditions.