In order to cut greenhouse-gas emissions and increase energy security, the European Commission stimulates the deployment of intermittent renewable energy sources (IRES) towards 2050. In an electricity system with high shares of IRES implemented in the network, energy balancing like storage is needed to secure grid stability and smooth demand satisfaction. Pumped hydro storage (PHS) is at this moment the best option for large scale storage. Switzerland has strong ambitions to further develop their PHS sector and become the battery of Europe. In this research, the potential of the Swiss PSH plants is explored, whilst taking inflow into the upper reservoirs of the PHS plants into consideration. To simulate electricity imbalance, Germany is used as a case study. Germany already has a high penetration of IRES and has plans to increase installed IRES capacity. By using an energy planning model (PowerPlan), three future scenarios of the German electricity system were designed, each with a different set of IRES installed (solar, mixed and wind). Results show that the Swiss battery ambition offers most benefits to a wind-oriented scenario, reducing both shortages as well as surpluses. Water inflow in Swiss PHS-reservoirs is of minor importance when looking at security of supply, although it was shown that the solar-scenario profits more from inflow in terms of system stability. However, a potential conflict was observed in the solar-scenario between the need for electricity storage and the storage of natural inflow, resulting in more surpluses in the system when inflow was taken into account.