The battery-ultracapacitor hybrid energy storage system (HESS) and its management have been widely investigated in recent years. Meanwhile, there is a lack of general and quantitative analysis on the energy loss of the battery-ultracapacitor HESS that does not depend on any specific control algorithm or physical limitations. In addition, the battery-ultracapacitor HESS is actually a simple example of a networked energy system. An agent-based control approach is desirable in order to improve the synergy, and thus, the flexibility, scalability, faulttolerance and reliability of the hybrid energy systems, and also the computational efficiency. Finally, considering the requirement of fast and frequent wireless charging, ultracapacitors could be more suitable than batteries due to their excellent reliability and charge/discharge capability. In this paper, these three aspects for the energy systems using ultracapacitors, i.e., analysis, control, and wireless charging, are discussed.