The performance of a plug-in hybrid electric vehicle (PHEV) or an electric vehicle (EV) is closely related to the performance of its high-voltage battery pack. This is why, among the various means of maintaining a battery's peak performance, the importance of thermal management is emphasized. Since the early stages of the development of Li-ion batteries, much emphasis has been placed on battery cooling in order to secure stability, while less attention has been given to battery heating. However, in a low-temperature environment, using a battery without heating it severely undermines the battery's performance and life expectancy. A PHEV or an EV operates with energy that is stored by charging the battery, which can then be heated by an external source in a low-temperature environment prior to driving. In this study, a battery HILS and an environment simulation system are used to verify that pre-heating a battery in a low-temperature environment, using an external source, such as a charging stand, improves the battery's performance as compared to circumstances in which this is neglected.