The first steps toward battery aging mitigation are aging detection and characterization. Cell-level signals that can be used for these purposes are few and, for the actual understanding of aging mechanisms, we often rely heavily on destructive, post mortem characterization. In this work, we focus on the relations between cell voltage, current, and temperature during battery cycling as well as dedicated in situ tests of differential voltage analysis (dV/dQ), incremental capacity analysis (dQ/dV), and electrochemical impedance spectroscopy (EIS). Through these tests, we further develop the understanding of how battery signals reflect internal electrochemical processes.Power-optimized cells with a blended Li x Ni0.5Mn0.3Co0.2O2 + Li y Mn2O4 (NMC-LMO) positive electrode and graphite negative electrode were cycled with constant current at mild (1.0C) and fast (2.7C) charge rates under room temperature (29 °C) and sub-ambient temperature maintained in a climate chamber (10 °C). Previous studies have shown the effects of surrounding temperature [T. Waldmann, M. Wilka, M. Kasper, M. Fleischhammer, and M. Wohlfahrt-Mehrens, J. Power Sources, 262 (2014)] and charge protocol [A. S. Mussa, M. Klett, M. Behm, G. Lindbergh, and R. Wreland Lindström, J. Energy Storage, 13 (2017)] on similar cells, and our protocol was designed to induce and seek in situ evidence for lithium plating.On the contrary, no plating is observed and several tropes regarding the temperature-dependence of aging are challenged. During cycling, the measured temperature at the skin of each cell is substantially greater than the surrounding temperature. By means of the techniques mentioned above, we observe loss of cyclable lithium by SEI growth as the dominant aging mechanism. This mechanism, however, is not accelerated by increased temperatures for this cell design, even with skin temperatures exceeding 50 °C.In addition to SEI growth, the particular conditions of mild cycle rate and sub-ambient temperature (1.0C, 10 °C) cause selective degradation of NMC that is not observed in other aging scenarios. Such selective degradation has been previously noted for this cell chemistry, though mostly through the use of destructive, post mortem techniques [B. Stiaszny, J. C. Ziegler, E. E. Krauß, J. P. Schmidt, and E. Ivers-Tiffée, J. Power Sources, 251 (2014)]. We show that it is possible to track this degradation using markers from simple in situ tests. This reveals that cells with similar capacity retention can have divergent aging behaviors and vastly different levels of practical performance, highlighting once more the importance of in situ aging characterization.Another point of interest of this experimental campaign is the relationship between cycle life and cell polarization. The longest cycle life (in terms of capacity retention) was for cells cycled under the most extreme conditions (2.7C and 10 °C) while the shortest was for those cycled under the mildest conditions (1.0C, 29 °C). This motivates us to question the paradigm of effective cell usage. Increasing polarization on a cell certainly decreases the energy available in each cycle, but this can ultimately protect the cell from long-term aging. Effectively, this represents a harsh but tunable compromise between power and energy densities. In certain cases of rapid charge and discharge, it may be suitable to forgo protections from polarization (e.g. battery heating or rate throttling) and sacrifice cycle energy in order to prolong the cycle life of a battery.