## 4 Results and Evaluation
### Assessing Energy Footprint and Battery Efficiency
After the above analysis, the consumption values  
Figure 14: Sensor node aggregate consumption-related measurement arrangements and results: (**a**) battery voltage graphs for node #A1 (red curve) and for node #A2 (blue curve) for a 5-day period; (**b**) the prototype real-time measuring system capturing the amperage consumption of the sensor nodes; (**c**) inspecting the idling and sleeping sensor node amperage consumption via the Serial Plotter tool; (**d**) inspecting and characterizing the stages of the sensor node activity, in real-time, via the Serial Plotter tool; (**e**) estimation/verification of the Li-Ion 18,650 battery life expectancy for sensor nodes via a practical online calculator; (**f**) battery voltage drop for node #A1 over a period of 42 days. depicted in Figure 14d conform satisfactorily to the electric characteristics of each soil instrument used, as presented in Section 2.1. After a random (in order to eliminate potential repetitive LoRa radio packet collisions) but bounded delay, both soil-specific and health status sensor node data were transmitted at the additional rate of 90 mA for a 100 ms time period. The LoRa transmitter was set to moderate settings (i.e., having a coding rate set to 4/5, bandwidth set to 128 kHz, spreading factor set to 7, and with the transmit power set to 14 dBm). The LoRa low communication rate was not an issue for the specific application case, as a few bytes had to be transmitted per sensor unit every 5 min at the fastest soil measurement periodic report rate scenario. The specific LoRa packet payload was close to 55 B. At this point, from the micro-analysis perspective, by arithmetically integrating the instantaneous consumption values during the activity period and dividing by the total activity duration (which as close to 4.20 s), an average current value close to 40 mA was calculated for modeling the node behavior during each measurement/transmission event. Given the close to 250 mA consumption for the close to 300 s sleep period and the utilization of a 2500 mAh battery and its 20% discharge capacity limit, an operation duration close to 104 days was extracted, and it can be verified by an easy-to-use online battery life estimator [43]. Figure 14e depicts exactly the parameters used and the corresponding battery duration results for the aforementioned case. Figure 14f illustrates the voltage drop (in volts) over time (in hours) for the 18,650 battery unit feeding node #A1. Figure 14f also contains a linear trend line and its fit estimation performance according to the R\({}^{2}\) metric. The match is very satisfactory, thus verifying the good behavior of the Li-Ion type of batteries. From a macro-analysis perspective, according to the typical Li-Ion battery behavior, as explained in recent work [44], the voltage, especially for small discharge rates (i.e., that match the below 100 mA current draw of our board), drops 0.7 V approximately from the fully charged to the 80% discharged battery status. In fact, taking under consideration the 0.0003 V/h voltage drop rate extracted by the experimental measurements in Figure 14f, this indicates a battery life duration of 97 days, which is close to the results of the micro-analysis (i.e., 104 days). The small difference experienced is justified by measurement and calculation process errors (like the quantization error of the auxiliary measuring circuit) and by manufacturing imperfections of the specific battery used. In all cases, the power and energy consumption equivalents could be easily extracted by the amperage (and each elementary activity duration) real-time data given that the sensor node system was supplied from a battery with a nominal voltage of 3.6 V. For instance, the soil instruments consumed (gross/net due to the charge pump and/or the multiplexer circuits) from 29 mW/13 mW to 173 mW/78 mW; the node idiled at 25 mW, and the transmission action via LoRa added 328 mW at 14 dBm.