Electric energy storage is probably the first viable for households since they pay the highest electricity tariffs, being a factor four higher than bulk electricity prices. The attractiveness depends on the subsidy systems (if existing), the electricity price and the purchase cost of a PV installation and a battery system. Since the electricity price may not remain constant during the lifetime of the storage system, a financial cash flow calculation is needed including discount rate and inflation. In this research the optimal PV-battery system is determined as a function of the remuneration (discerning a subsidised region, a “market” price region and no fees at all), the investment year (2012, 2017 and 2021) and the electricity price increase rate (0%, 4%, 6%) (including the general inflation rate). The analysis is based on available battery energy storage systems on the market and on real household measurement data. All these degrees of freedom secure the accuracy of the analysis. The article shows also the battery throughput cost with a direct comparison to the electricity cost. It becomes clear that batteries can already be cost-effective today without subsidies and irrespective of the electricity price increase, but without a return on investment if the electricity price does not increase more than the inflation. An investor cannot recommend batteries today. However, if the electricity price increases with 4% than batteries become quickly attractive and do not need subsidies.