As part of the U.S. Environmental Protection Agency (U.S. EPA) “Midterm Evaluation of Light-duty Vehicle Standards for Model Years 2022-2025”, the U.S. EPA is testing 12 volt lead-acid batteries and assessing the effectiveness of stop-start technology for evaluating low cost CO2 Green-House Gas (GHG) reduction technology. Stop-start has been popular in Europe due to high fuel prices and the stringent EU CO2 emission target established in 2009. In 2014, about 60 to 70 percent of vehicles sold in the European market offered the stop-start technology. Vehicles with sufficiently smooth and seamless stop-start technology have been well-received by consumers, especially when paired with some explanation of the system’s benefits and operating characteristics at the time of delivery. With these more recent implementations, it is more common now for stop-start systems to be applied as standard equipment on high-volume vehicles like the Chevrolet Malibu, Chrysler 200, Jeep Cherokee, and Ram 1500 truck. Ford expects to offer it on 70 percent of its North America vehicle lineup by 2017, including the 2015 F-150 truck. The introduction of stop-start has stimulated development of 12V battery systems capable of providing the enhanced performance and cycle life durability that it requires. Much of this activity has involved advanced lithium-ion chemistries, variations of lead-acid chemistries, such as absorbed-glass-mat (AGM) designs and lead-carbon formulations. Several AGM lead-acid batteries for start-stop technology were tested to characterize the battery pack performance, internal resistances and capacitances at the Battery Test Facility (BTF), United States Environmental Protection Agency (EPA) in Ann Arbor, Michigan. This paper presents the lead-acid battery pack model development and validation integrated into EPA's ALPHA vehicle simulation model. The battery pack model consists of a battery cell, a thermal and, SOC, Resistance-Capacitance (RC) electric circuit. The battery resistances and capacitances were calculated by using the EPA in-house 95Ah GM Malibu lead-acid battery test data. The lead-acid battery library in the ALPHA model was validated with 2010 Mazda 3 iStop and 2010 VW Golf TDI vehicle data obtained from ANL chassis dynamometer tests. The simulated battery voltages, currents, and State of Charge (SOC) are in excellent agreement with the vehicle test data on a number of drive schedules.