High power lithium-ion batteries need to exhibit long service life to meet targets of automotive applications. This article describes the deep investigation of the so-called VL6P cells, high power lithium-ion cells mass produced by Johnson Controls – Saft (JC-S), in order to understand the root causes of their aging. Cells aged by calendar and cycle life are investigated here compared to fresh cells. Among the results of the different analyses, the most significant is that more active lithium is detected in negative electrode after aging. This tends to indicate that effect of aging is due to increase of positive electrode limitation. Results of this investigation will allow JC-S to continue to improve life of the lithium-ion cells.