The growing reliance on batteries across diverse applications highlights their essential role in everyday life. In an increasingly electrical world, it is crucial that Lithium-ion Batteries (LIBs), known for their high energy density and extended cycle life, can be understood and utilised for optimal performance. Having a Battery Management System (BMS) that can provide accurate state determination is therefore essential. Among the various models discussed in the literature, the focus often narrows down to 1RC and 2RC Electric Equivalent Circuit Models (EECMs), due to their widespread use and capability to accurately represent the nonlinear behaviour of batteries. This provides a balance between high estimation accuracy and manageable computational complexity, making them suitable for real-time applications, while aligning with the practical requirements of online battery management systems. With three to six …