A statistically designed accelerated aging experiment was conducted to investigate the effects of aging time, temperature, and state-of-charge (SOC) on the performance of lithium-ion cells. In this experiment, a number of cells were stored in a variety of static aging environments ranging from 25°C and 60% SOC to 55°C and 100% SOC. The power output of each cell was monitored regularly over the course of 44 weeks via a low current level hybrid pulse power characterization test. A single empirical model of power fade, involving two concurrent degradation processes, was found to be applicable over a wide range of experimental conditions. The first degradation process is relatively rapid (nearly complete within 4 weeks) and is accelerated by temperature with unknown kinetics. The second degradation process (accelerated by temperature and SOC) is less rapid and exhibits time3/2 kinetics.