The objective of the study is to develop a methodology to define the optimal operating strategy of a battery energy storage system (BESS) on the end-customer's premises that delivers him/her the maximum annual profit. The applications considered are peak shaving and frequency regulation in the FCR-N hourly market. The methodology is applied to a large group of actual end-customers with hourly measured electricity consumption. The results indicate that the operating strategy depends strongly on the shape of the end-customer's load and the reward level in both applications. Finally, the sensitivity parameters and further research needs are listed.