Utility scale stationary battery storage systems, also referred to as front-of-the-meter, play a key role in the integration of variable energy resources providing at the same time the needed flexibility. Battery storage increases flexibility in power systems, enabling an optimal use of variable electricity sources like photovoltaic and wind. Batteries can provide services for system operation, defer investments in peak generation and grid reinforcement. Utility-scale battery storage systems have a typical storage capacity ranging from few to hundreds of MWh. Different battery storage technologies, such as lithium-ion (Li-ion), sodium sulphur and lead acid batteries, can be used for grid applications. In recent years, Lithium-ion battery storage technology is the most adopted solution.