# Power Sources for Unmanned Aerial Vehicles: A State-of-the Art
## 2 Unmanned Aerial Vehicle (UAV)
### Battery-Based Supply Techniques  
#### 2.2.1 Battery-Powered Unmanned Aerial Vehicles (UAVs)  
Battery power is widely utilized in small UAVs, especially quadrotors, as it offers simplicity and flexibility to the propulsion system [71]. Battery-based platforms, particularly those using lithium batteries, such as LiPo batteries, are popular in hobbyist and  
Figure 3: UAV propulsion system block diagram. commercial applications due to their flight time capabilities and cost effectiveness. However, the endurance of small battery-powered UAVs is limited by the weight constraints of the battery pack, typically allowing for a maximum flight time of around 90 min using LiPo batteries [46]. LiPo batteries are preferred for small UAVs due to their lightweight nature and relatively high specific energy. In fact, LiPo batteries power the majority of micro aerial vehicles weighing less than 2 kg and with a length below 100 cm [30]. In selecting the appropriate battery technology for a given UAV application and mission, various characteristics such as specific energy, energy density, and specific power are taken into consideration. Table 1 provides detailed information on these characteristics for four different battery technologies, aiding in the battery technology selection process [44]. Additionally, in a specific study, different battery technologies were assessed based on the state of charge (SOC) for a particular mission, further emphasizing the importance of considering mission requirements when choosing battery technologies [58]. Ref. [74] focused on examining the factors that affect the performance of UAVs powered by batteries. Mathematical equations were developed to assess the UAV's range and endurance, taking into consideration the discharge conditions of the battery. The study establishes relationships to estimate the range and endurance of battery-powered aircraft, considering battery discharge rate and voltage drop effects. The research demonstrates that the Peukert effect can enhance range and endurance, particularly when battery capacity significantly exceeds current demand. Conversely, when the current draw approaches the battery's nominal capacity, effective capacity decreases. In situations with geometric constraints and a fixed battery weight as a fraction of the total aircraft weight, increasing battery capacity can lead to reduced performance due to higher power requirements and current draw. One of the main challenges encountered by electric vehicles relying on battery power, including UAVs, is the limited autonomy they possess. Extensive efforts have been devoted to enhancing the performance of batteries in order to prolong operational duration and enable extended missions for electric vehicles. Despite the advancements made in battery technology, the specific energy of current batteries still poses limitations on the endurance and range of UAVs, which may not meet the requirements of numerous UAV applications. Additionally, improvements in energy density can have implications for the stability and safety levels [75]. To tackle these limitations, various solutions have been proposed in the existing body of literature. Fuel cells have emerged as a promising alternative due to their higher specific energy. Furthermore, numerous existing UAVs employ a hybrid configuration in their power supply, utilizing multiple energy sources such as batteries, fuel cells, solar cells, and supercapacitors. In practice, hybrid configurations integrate various power sources, such as batteries, fuel cells, solar cells, or generators, to work in harmony. The energy management system (EMS) plays a crucial role in optimizing power distribution among these sources to achieve enhanced efficiency and endurance [76]. The advantages of hybrid configurations over single-source systems are numerous. They offer improved endurance, as different sources can complement each other. For example, batteries can provide immediate power for take-off, while fuel cells or generators can sustain operations for longer durations.