This study introduces a nonlinear autoregressive with exogenous inputs (NARX) model for identifying lithium-ion battery systems to optimize performance, safety, and lifespan in applications like electric vehicles and renewable energy. Experimental validation shows that the NARX model outperforms traditional linear models by accurately predicting battery behavior, even under dynamic conditions. The research highlights the importance of nonlinear modeling in capturing the intricate relationships among state-of-charge, voltage, and current, while also discussing the challenges related to the practical implementation of the model.