This paper presents results obtained from extensive accelerated lifetime tests performed on a high power Lithium Titanate Oxide (LTO) battery cell. The tests were performed at elevated temperatures, with different C-rates, and for different cycle depths. The obtained results have shown a very good capacity retention and a reduced internal resistance increase (and subsequently reduced power capability decrease) even after more than 8000 cycles performed at 42.5°C. We found out that both the capacity and the internal resistance have been degrading faster when the LTO-based battery cells were cycled with a smaller C-rate (i.e., 1C) than with a higher C-rate (i.e., 3C). Moreover, based on the harvested aging results, we discovered that the capacity and not the internal resistance is the performance parameter of the tested LTO-based battery cells, which will limit their lifetime.