# In Operando Health Monitoring for Lithium-Ion Batteries in Electric Propulsion Using Deep Learning
## 4 Results and Discussion
### In-Air Current and Voltage Profile Measurements  
Figure 7 illustrates the current and voltage readings collected by the newly developed BMS during in-air testing. For each in-air cycle, the current drawn by the quadcopter varied randomly based on the power needs of the quadcopter, as shown in Figure 7a. As depicted in Figure 7b, the charging of the LIB was conducted on the ground, similar to the process in Figure 4. Figure 7b represents the first cycle of in-air testing. At the end of the charge, 0.167 \(\pm\) 0.03 h were required to prepare for the flight, which included integrating the BMS with the quadcopter and setting up the flight station, as shown in Figure 3c.  
At the beginning of the flight, the current drawn from the battery increased sharply until it reached the required power for the electrically propelled quadcopter, which in this case was approximately \(-\)6 A. Once the required power was reached, the current drawn remained relatively consistent, with slight fluctuations during the flight to maintain the quadcopter's attitude and altitude. At around 0.167 h, the current drawn dropped rapidly  
Figure 6: Surface temperature data for a 4-cell NCA battery pack, with ambient temperature (TA) logged by BMS. (**a**) Data of 42 cycles performed on the ground. A repeated pattern is observed, with T4 reaching the highest temperature of 38 \({}^{\circ}\)C. (**b**) The third complete cycle performed on the ground. Temperature peaks are observed at the end of the constant current phases for both charging and discharging.  
to zero due to a temporary cut-off in power to adjust the flight's attitude. Upon restarting the experiment, the current drawn increased again, reaching 9 A. The spikes in the current profile before the end of the experiment were due to corrections made to the quadcopter's attitude. The rise in voltage observed during these attitude corrections was considered an outlier in the data.  
The current drawn by the quadcopter to maintain attitude and altitude increased over the 20 cycles conducted in-air, as shown in Figure 7a. The discharge current started at a maximum of \(-10\) A for the first experiment and increased over time, reaching the highest discharge current of 13 A by the ninth in-air cycle. For the last 14 cycles, the current drawn from the battery was consistently above 11 A. The current drawn from the batteries during in-air testing occurred at higher C-rates compared to the on-ground experiments, and the BMS could record these high C-rate currents accurately drawn from the batteries, which were higher C-rates than the on-ground experiments. The BMS could record the currents at high C-rates.  
Figure 7: Current and voltage data collected by BMS during random flight patterns of the drone. (**a**) The current and voltage over 20 cycles performed by the drone. The battery pack provides variable discharge current necessary for flight. (**b**) One discharge cycle during flight (the first of 20 cycles). During this cycle, the current discharges at higher C-rates in real-time, while the voltage drops from 16.8 V to 10 V. Note that each discharge cycle lasts less than an hour.