## 4 Discussion  
The e-HPS represents an innovative option for the retrofit of the ICE-HPS in conventional industrial trucks. The practical realization of the e-HPS considered the perfect interfacing of the four subsystems: cabin-control unit, electric motor/converter/hydraulic pump, battery pack/battery management system (BMS), and battery charger. The chosen components are easily available and ensure a high efficiency system. The Arduino-nano was revealed to be a reliable control unit and, through the Can-Bus communication protocol, allows all of the devices to work together in an efficient and safe way. The realized e-HPS is made of affordable components and their connection layout is descriptive at a practical level, reproducible, simple, and effective.  
The electric power measurements quantified the daily power consumption, allowing estimation, using the KiBaM model, of the SOC of the battery pack after the collection scenario time. The results of the KiBaM model were extended to forecast the end-of-life time of the battery pack by analyzing the corresponding SOH. The obtained results are in accordance with the performance of the lithium-ion battery technology presented in the related literature.  
Regarding the battery pack, this study indicates that the number of battery cells should be as low as possible, while maintaining a good safety margin of the SOC, that is, generally over 20% [48]. In this study, 1680 cells resulted in 30% of the SOC remaining after the collection scenario activities, ensuring the battery's end-of-life of 1500 charge/discharge cycles and only two battery pack replacements within the truck lifespan.  
The economic analysis highlighted that, although the e-HPS requires an initial cost to be realized, the resulting fuel savings allow the investor to save about \(\xi\) 65,000 over 12 years. Furthermore, results show that the total CO\({}_{2}\) emissions for the e-HPS are about 80% lower than those for the ICE-HPS. This last point leads to two reflections:  
* In general, CO\({}_{2}\) emissions are associated mainly with the idling phase rather than with the traveling phase.
* Equipping the work truck with the proposed e-HPS could be an effective option to reduce CO\({}_{2}\) emissions and fuel consumption rather than realizing a full electric compactor truck, including an electric powertrain for traction, particularly during the transition phase from thermal to electric vehicles, when a high number of thermal work trucks are already built and registered. Furthermore, conversely to the ICE-HPS, the e-HPS would fit perfectly with two technologies:
* the consolidated start-stop system, now present in almost all commercial and work vehicles;
* the emerging vehicle-to-grid (V2G) system that considers vehicles, equipped with a battery pack, as grid storage units to sell demand response services by either returning electricity to the grid or by favoring their charging rate.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Activity** &
\begin{tabular}{c} **Total Diesel Fuel** \\ **Consumption (L)** \\ \end{tabular} & **Total CO\({}_{2}\) Emissions (kg)** \\ \hline Traveling (ICE-HPS) & 10,452 & 27,886 \\ \hline Idling (ICE-HPS) & 56,345 & 150,329 \\ \hline
**Total for ICE-HPS** & **66,797** & **178,214** \\ \hline Traveling (e-HPS) & 10,452 & 27,886 \\ \hline Idling (e-HPS) & 0 & 0 \\ \hline
**Total for e-HPS** & **10,452** & **27,886** \\ \hline \hline \end{tabular}
\end{table}
Table 4: Diesel fuel consumption and CO\({}_{2}\) emissions during the vehicle lifespan.