The global effort to reduce fossil fuel consumption implies massive energy storage exploitation. The only available technology able to satisfy the required performance is the Li-ion cell. To ensure a sustainable cycle life, it is necessary to exploit the batteries during their overall possible lifetime. BAT-MAN is a project by Brain Technologies to provide a product that offers an online, real-time, and non-intrusive estimation of a lead-acid battery's charge status and state of health. The thesis aims to provide an extension of BAT-MAN to Li-ion batteries. The thesis aims to investigate the behavior of different Li-ion cells to build a general model for simulation and identification purposes.