The energy transition in the electrical energy supply sector is leading to a steadily increasing share of fluctuating renewable energy sources in the power grid. Thus, control reserves such as frequency containment reserve are gaining in importance and need further investigation. In Germany, the power grid is divided into balancing groups, in which supply and demand must be balanced out. The provision of frequency containment reserve, creates an energetic imbalance in the respective balancing group depending on the grid condition. However, this imbalance and the resulting costs for the balancing group manager are further to be quantified. This work provides a simulation model that examines the energetic imbalances resulting from the provision of frequency containment reserve. We validate the simulation results with field-data from the operation of a 6 MW battery storage system and derive the resulting cost for the energy imbalances. In addition, flexibility options for batteries given by the regulatory framework in form of the degrees of freedom are evaluated. The results show, that the degrees of freedom enable a battery storage operator to additionally charge or discharge up to 9 MWh per MW frequency containment reserve per month on average. The additional profits from the German imbalance settlement price are on average 615 € per MW frequency containment reserve per month for non-use of the degrees of freedom. In Conclusion, the field-data confirm the simulation data in terms of energy deviations in the balancing group due to the provision of FCR. Over the period of one month, the deviation usually leads to a cost-related advantage for the balancing group manager. The provision of frequency containment reserve as a grid service can therefore be seen as a positive gain for a balancing group.