The provision of frequency containment reserves (FCR) by electric vehicles in an autonomous port transportation system is a way to stabilize power grid frequency. However, the Vehicle-to-Grid (V2G) service's additional charging processes lead to faster degradation of vehicles' batteries. How much the FCR provision affects battery life (BLD) and what degradation costs are incurred depends on specific application conditions. Therefore, this study demonstrates the application of a V2G system for a port container terminal. In the analysis, vehicles' charging processes with and without FCR provision are simulated within the degradation model developed for this case, and relevant degradation factors are determined by applying the Rain-Flow Counting (RFC) method. Overall, three degradation models are discussed concerning their fit for the case at hand. Results indicate that Cycle-Count Models best represent battery degradation, showing an increase in battery degradation of 1.36% through the use for FCR. This supports improved business case simulations to enable two-sided sustainability models by stabilizing the electric grid and enabling electric transportation in ports simultaneously.