This study mainly focused on evaluating the activation energy of LiFePO4 batteries by using a novel dual dynamic stress accelerated degradation test, called D2SADT. This test method was developed to simulate a situation involving driving an electric vehicle in the city. D2SADT contains two controllable dynamic stress variables: the environmental factor corresponding to temperature cycling and the power factor corresponding to charging-discharging currents and times at which they were implemented simultaneously. A reference power test was performed repeatedly at a certain time (e.g., five temperature cycles), and the cell capacity was then calculated to monitor the degradation of the batteries. A physical-based reliability model called Norris-landzberg equation was applied to compute the activation energy which is the indicator to explain the degradation behavior of the Li-ion battery using D2SADT. The test results indicate that the activation energy decreases when the capacity loss (before 10%) increases. It is concluded that the power fade may be accelerated when the charge-discharge cycle increases for the LiFePO4 battery operated a specific power-and-temperature cycling condition. The test is ongoing and the updated results are under analysis to help us understand the degradation mechanism of Li-ion batteries by more realistic test conditions.