This work proposes a novel framework for evaluating the second- and third-life viability of lithium-ion battery packs through the development of the RISE Index—a comprehensive metric based on Resistance growth, Integrity, Safety, and End-of-life usability. While previous research focuses on singular indicators such as residual capacity or State of Health (SoH), these approaches lack a unified, safety-informed structure for reuse qualification. This paper distinguishes itself by integrating multiple aging indicators, including resistance evolution, degradation theory, and thermal safety considerations, into a consolidated decision-making tool designed for practical deployment. The novelty lies in the formulation of the RISE Index, which fuses empirical data with electrochemical degradation mechanisms such as SEI formation, lithium plating, calendar aging, and cycling-induced impedance growth. The methodology includes a comparative analysis of Nickel Manganese Cobalt (NMC) and Lithium Iron Phosphate (LFP) chemistries using Electrochemical Impedance Spectroscopy (EIS), Direct Current Internal Resistance (DCIR), and model-based estimation to characterize resistance trends under varied operational conditions. Theoretical models for impedance growth link internal changes to observable resistance behavior. Findings indicate that LFP cells offer superior thermal and impedance stability, while NMC requires stricter monitoring due to accelerated resistance growth. The RISE Index enables stakeholders to classify and prioritize used battery packs for safe and efficient second- and third-life use, thereby addressing a critical industry gap. This integrated approach represents a significant advancement over prior work by embedding safety, usability, and degradation science into a unified lifecycle optimization framework.