Energy is the essential resource for modern society, but recent growing concern over limited fossil-fuel resources, pollution, and global warming by greenhouse gas emissions has introduced the need to use renewable energy at a large scale, together with the widespread use of HEVs and EVs. Among energy storage technologies, Li-ion batteries, backed by their success in electric vehicles and associated mass production, have gained interest for stationary applications because of their high energy/power density and greater than 90% energy efficiency. Currently, 77% of electrochemical ESSs operated for grid stabilization in United States use Li-ion batteries-mostly for frequency regulation service, which is a high-value market. To maximize benefits, the use of single Li-ion battery chemistry for both stationary as well as electric vehicle applications is being considered. Because of the dual use of Li-ion batteries in electric vehicles (EVs) and in stationary applications, this study focuses on the performance and degradation of two different Li-ion battery chemistries when exposed to (1) selected grid services, (2) typical EV use patterns, and (3) a combination of grid services and EV applications, sometimes referred to as vehicle to grid (V2G). Therefore, high-energy LiNi_0.8Co_0.15Al_0.05O₂ (NCA) and high-power LiFePO₄ (LFP) based advanced Li-ion battery chemistries were chosen for our reliability studies under three scenarios: (1) frequency regulation, and EV drive cycle coupled with either (2) frequency regulation or (3) peak shaving to understand the degradative effect of grid service that can increase lifecycle cost. The NCA-based cell has good power and energy characteristics and has been used in EVs, but it tends to release significant amounts of oxygen from its cathode, resulting in oxidation of the electrolyte and thermal runaway. In contrast, the LFP-based has been widely deployed for stationary energy storage because the LFP electrode provides high power, stability, and does not generate oxygen during heating; thus, safer than the NCA electrode. The reliability of these two battery chemistries was evaluated by analyzing lifecycle performance factors such as capacity/energy fade, round-trip efficiency (RTE), resistance change, and calendar aging behavior will be presented.