Commercially available, high power lithium ion batteries with capacities of about 3 Ah, on basis of different cell designs and mainly pouch format (but also one round cell) are cycled under continuous high discharge currents, up to 45C, to test for actual power capability. Using a different batch of cells, in addition low rate cycling tests (1C discharge) are carried out and compared to the respective high power procedures. Impedance measurements are conducted for full cells in their fresh and aged state. In addition, all cells are disassembled in their fresh and end of life states to gain further understanding on correlation of cell design (e.g. cell chemistry, electrode thickness, composition of active coating) and aging mechanisms. Therefore, the cells and electrodes are examined optically and characterized by means of XRD and SEM. It is found that there is a wide spread in quality of commercially available cells in terms of power capability, performance and aging. Aging mechanisms are discussed for all tested cells, and also the effect of high power vs. low power cycling. Aspects like SEI growth, change in particle size, cracking and impedance rise are systematically investigated and discussed.