Degradation and health monitoring of lithium-ion batteries is explored through life-cycle testing and failure analysis. Test samples comprised of four different battery types from two different manufactures underwent aging and charge/discharge cycling using a variety of load profiles including constant current discharge, pulsed discharge, and varying depths of discharge. Data from in situ monitoring of several parameters including current, voltage, temperature and internal resistance, was analyzed in order to find the best features that could be used to track and characterize battery performance degradation. Degraded samples were disassembled according to a newly developed disassembly methodology that considered the effects of the environment on post-disassembly failure analysis results. Several different failure analysis methods were used in order to gain an understanding of how degradation mechanisms propagate from a materials stand point. Battery electrodes were investigated to observe changes in their chemical and mechanical structures.