The thermal behavior of pouch-type lithium-ion batteries during discharge and charge cycles is investigated by numerical simulation. A transient thermal model using finite element method software is developed through the modification of an electrochemical-thermal model. The developed model is validated with experimental data. For the experiment, a 304252 pouch cell is fabricated and tested in the laboratory. This model captures the dynamic responses of temperature, and distributions of current density and temperature, during discharge and charge cycles. Our results indicate that the discharge temperature is higher than the charge temperature at cut-off voltage. The temperature distribution upon discharge is similar to that of charge. On the other hand, different temperature distributions are observed at various C rates. The temperature profiles obtained from modeling and experiment are in good agreement.