This study has examined what services grid-connected energy storage systems can provide to the electricity grid in Sweden. In particular, energy storages in the form of batteries have been examined. This has been done by studying existing literature and current installations of grid-connected batteries. A total of 13 different services were identified: arbitrage, capacity firming, curtailment minimization, electric supply capacity, black start, frequency regulation, voltage support, transmission and distribution congestion relief, reduced transmission grid costs, increase of self consumption, end-consumer power quality, time-of-use bill management and backup power. Furthermore, a grid-connected battery storage system that will be installed by Vattenfall was modelled and simulated in this paper. The results showed that the battery storage system can mitigate congestion in the transmission grid, as well as providing the grid with frequency regulation. This can generate a revenue of 3 million SEK annually.