This is why Hybrid Energy Storage Systems (HESS) have become an interesting approach to provide both energy and power intensive responses by combining and using (by proper management algorithms) the best performances offered by two or more storage technologies. Different types of battery technologies show performances suitable for providing multiple grid services such as peak demand response, frequency and voltage regulation, load-levelling, backup power, and balancing the effects of locally intermitent renewable sources (i.e. wind and solar). However, it is an accepted common concept that no ‘one size fit all’ solution is currently available, able to be the best one in a wide range of services and applications.