## 4 Results of Measurements
It should also be noted that the large amplitude values of the individual harmonics corresponded to very strongly distorted waveforms of input current I\({}_{\text{in}}\) regardless of the SoC of the mobile device battery. Figure 9 shows the waveforms of input current I\({}_{\text{in}}\) (a) and the input current spectrum (b) as a function of the battery SoC used in Notebook. The output voltage V\({}_{\text{out}}\) of the dedicated charging circuit during the battery charging process was approximately 20 V.  
Analyzing Figure 9a, it should be noted that a lower peak-to-peak value of input current I\({}_{\text{inpp}}\) = 0.62 A was obtained for SoC equal to 90%, while for SoC equal to 10%, the peak-to-peak current value was higher at 0.83 A, which is related to the start of the charging process of the battery used. As the SoC of the battery increased, the charging current decreased. It can also be seen that the waveform of the input current I\({}_{\text{in}}\) was still far from a sinusoidal shape. Analyzing Figure 9b, it should be noted that, regardless of the SoC level of the Notebook battery, the spectrum of the input current contained large normalized values of consecutive harmonics. For SoC = 10%, we can observe that as many as nine harmonics of the fundamental frequency had a value significantly close to the maximum amplitude. It should also be noted that the large values of the amplitudes of the individual harmonics correspond to highly distorted waveforms of the input current drawn from the power grid regardless of the SoC level of the Notebook battery. Figure 10 compares the waveforms of input current I\({}_{\text{in}}\) (Figure 10a) and the input current spectrum (Figure 10b) for two arbitrary selected loads in the form of mobile device batteries Smartphone and Notebook, respectively. The output voltage V\({}_{\text{out}}\) of the charging system during the charging process of the Smartphone battery was equal to approximately 9 V, while that of Notebook was equal to approximately 20 V. The SoC level of both the batteries during the analysis of the waveforms of input current I\({}_{\text{in}}\) and the spectrum of the current under test was equal to 50%. Analyzing Figure 10a, it can be seen that the recorded input current waveforms are heavily distorted and do not resemble a sinusoidal waveform in their shape. It should be noted that the highest peak-to-peak value of the input current (I\({}_{\text{inpp}}\) = 0.82 A) was obtained for the charging system loaded with the Notebook battery, while when using the Smartphone battery as the load, the current value was 45% lower and amounted to I\({}_{\text{inpp}}\) = 0.46 A. The different peak-to-peak values of input current I\({}_{\text{in}}\) are the result of the different power supplied to the batteries of the selected mobile devices during the tests. In Figure 10b, it should be noted that the spectrum of the input current waveform contains significant normalized harmonic values. In the case of loading the tested system with the Smartphone battery, we can observe that as many as nine harmonics of the fundamental frequency contained a value significantly close to the maximum amplitude. It should also be noted that the large values of the amplitudes of the individual harmonics correspond to highly distorted waveforms of input current I\({}_{\text{in}}\) drawn from the power grid regardless of the type of load. It can also be noted that the 30 harmonic bars of the fundamental frequency are presented in the experimental study, and the value of the amplitude of 30 harmonic bars is quite high at about 15% of the amplitude of the first harmonic bar. Comparing the results presented in Figures 8-10, it can be seen that for the load containing a smaller capacity battery (Smartphone), much larger distortions were visible than for Notebook. It can also be seen that the input current distortions were smaller at higher SoC values. It is also worth noting that the value of the battery charging current also depends on the value of its internal resistance.