Vehicle electrification is one of the most important emerging trends in the transportation sector and a necessary step towards the reduction of polluting substances and greenhouse gas (GHG) emissions. However, electric vehicles still present some environmental criticalities, such as indirect emissions related to the electricity used for charging the traction battery, which depends on the considered national electricity generation mix. The leading approach for quantifying the potential environmental impacts is the Life Cycle Assessment (LCA), a standardized methodology that takes into account the whole life cycle of a product, including production, use phase, and end-of-life. Among them, the use phase is the most controversial and heterogenic part of the battery LCA, being environmental impacts depending on different national electricity generation mixes and several factors difficult to estimate, such as charge-discharge power losses that provide significant contributions to the overall environmental impacts of the battery system. The purpose of this research is to conduct an LCA to investigate the Global Warming Potential (GWP) impact category associated with the use phase of two battery packs based on different NMC batteries but equivalent total capacity, equipping the same powertrain of an A-segment battery electric vehicle (BEV). The overall GWP ranges between 45.4 and 47 gCO2eq/km and total power losses between 2.5 and 3.19 gCO2eq/km, respectively. Finally, the M50LT battery model results in a greater GWP impact up to 3.5% than the 40T battery type.