As part of the midterm evaluation of the 2022-2025 Light-Duty Vehicle Greenhouse Gas (GHG) Standards, the U.S. Environmental Protection Agency (EPA) developed simulation models for studying the effectiveness of 48V mild hybrid electric vehicle (MHEV) technology for reducing CO2 emissions from light-duty vehicles. Simulation and modeling of this technology requires a suitable model of the battery. The goal of this thesis work is to define an equivalent model of a lithium-ion battery (LiF eP O4) 48V for mild hybrid applications, which is able to correctly simulate its behavior. The battery model is a standard equivalent circuit model with the two-time constant resistance-capacitance (RC) blocks.