Information on battery internal temperature is valuable to enhance the understanding of thermo-electrochemical reactions, to validate simulation models, and to refine battery thermal design. In this study, 12 thermocouples are embedded at strategically-chosen locations inside a 25 Ah laminated lithium-ion battery. Another 12 thermocouples are attached at the corresponding locations on the surface. The temporal and spatial variations of the temperature are measured at a series of discharge rates under different thermal conditions. The thermal response of these locations is also analyzed. The major findings include: First, the internal temperatures could differ from the surface for as large as 1.1 °C, even for a thin laminated cell. Second, the time constants of thermal response at the internal locations are generally dozens of seconds larger than on the surface. Third, the internal variation in the plane direction reaches above 10 °C under adiabatic 1.5 C discharge, much larger than in the through-plane direction, indicating the in-plane heat conductivity needs improvement. Finally, forced convection is effective to suppress the temperature rise as well as the variation. The direct measurement of internal temperature initiated in this study paves the way for implanting sensors/microchips in single cell to extract multiple physico-electrochemical signals simultaneously.