**4. Results and Analysis**

### *4.1. The Impacts of Battery Aging*

Figure 5 shows the results of electrical behaviors and the parameter variations of the batteries under thirteen aging stages (from the fresh to deep aged battery). It can be seen that the internal resistance increases significantly with the deep aging of the battery, however, the polarization internal resistance and polarization capacitance do not show obvious change regulations. The varying battery parameters are used to design the control parameters in optimal EMS; therefore, the EMS can be adaptive to the battery aging process according to the current SOH value. The results of the parameters in aging expression are provided in Table 3. The driving cycles of UDDS and Extra Urban Driving Cycle (EUDC) are used to assess the increased energy consumption induced by the battery aging. Compared with the fresh battery, the deep aged battery (SOH = 79.34%) cause extra energy cost of 15.19% and 14.28% under UDDS and EUDC, respectively.

**Figure 5.** Aging characteristics of batteries under thirteen different states of health (SOH) conditions: (**A**,**B**): test results of battery voltages and currents under urban dynamometer driving schedule (UDDS) driving cycles; (**C**–**F**): the varations of the battery parameters caused by the aging.


**Table 3.** Battery model parameters under the varying SOH phases.

For ease of designing the adaptive control algorithm, we wish to find out the main parameters (among the multiple battery parameters) that contribute the most to energy consumption. Therefore, the specific impacts of each battery aging parameters on increased consumption cost are further analyzed, in which the percentage of cost increment is calculated. The results are shown in Figure 6. The results illustrate that the capacity loss and resistance increase are the main factors leading to the increase of energy consumption. The capacity degradation accounts for up to 10.24% of the aging-caused energy cost while the internal resistance accounts for up to 6.42% of the aging-caused energy cost. On the contrary, the influences of OCV and RC items are minor (less than 0.29%) and can be neglected.

**Figure 6.** Specific impacts of battery aging on vehicle energy cost: (**a**) simulation at Extra Urban Driving Cycle (EUDC); (**b**) simulation at UDDS driving cycle.
