A Battery Test Facility (BTF) has been constructed at United States Environmental Protection Agency (EPA) to test various automotive battery packs for HEV, PHEV, and EV vehicles. Battery pack tests were performed in the BTF using a battery cycler, testing controllers, battery pack cooler, and a temperature controlled chamber. For e-machine testing and HEV power pack component testing, a variety of different battery packs are needed to power these devices to simulate in-vehicle conditions. For in-house e-machine testing and development, it is cost prohibitive to purchase a variety of battery packs, and also very time-consuming to interpret the battery management systems, CAN signals, and other interfaces for different vehicle manufacturers. Therefore, there is a need to accurately emulate battery pack voltage, power, current, State of Charge (SOC), etc. for testing e-machines as well as performing real-time HIL (Hardware-In-Loop) vehicle simulations by having the ability to instantly select a cell chemistry along with battery pack configuration such as cell capacity, number of cells in series/parallel, coolant type, etc.This paper presents lithium-ion battery pack HIL development and validation integrated into the EPA Battery Test Facility. The battery pack HIL model consists of lithium-ion cell chemistries, thermal characteristics, battery management system (BMS), and power limit controls. The HIL model of lithium-ion battery pack was validated by simultaneously running a real lithium-ion battery pack with Nissan Leaf EV and GM Volt Range Extended Vehicle power profiles to the battery cycler in the BTF. The emulated battery voltages, currents, SOC, and battery pack temperatures are in excellent agreement with battery pack test data on FTP UDDS, highway (HWFET) and US06 drive schedules.