Energy storage is a key component to obtaining cost-effective energy systems. Likewise, highly reliable storage systems are essential for guaranteeing safety and confidence in renewable energy systems across multiple geographical scales. In particular, energy storage systems (ESS) provide energy-integrated systems (ESI) with greater flexibility, simplifying coupling and interfacing Multiple Agents. Subsequently, to address some of the technological limitations of ESS in ESI, in this chapter, a thorough analysis of state-of-the-art electrochemical ESSs is presented. Firstly, some of the commonly used energy storage technologies are introduced. Lithium-ion batteries, supercapacitors, and redox flow batteries are some revisited technologies. Then, constructive details and required operating conditions to guarantee maximum efficiency and reliability standards are detailed. In the second place, practical aspects, bonded with the existing limitations of ESSs in multi-energy systems (MES) are described. To that end, some of the required energetic constraints and associated states are defined and briefly analyzed. For instance, the safe operating area, state of charge, state of health, and remaining-useful-life amongst other key energetic indicators are briefly described. Thirdly, considering the latter-mentioned constructive and functioning limitations of ESS, novel approaches designed to guarantee efficiency, security, and reliability, minimizing the impact of ESS in ESI and maximizing their useful life and economic profitability, are presented.