The stackable lithium battery energy storage system uses high-cycle-life lithium iron phosphate (LiFePO₄) batteries and a high-performance BMS to protect and manage the battery system. Each stack supports up to 6 modules, and multiple stacks can be connected in parallel to form a maximum of 15 battery modules in total. The capacity can be flexibly configured, and when paired with a photovoltaic (PV) system, it can meet a wide range of power demands for both residential and industrial applications.