Electric buses (EBs) play a crucial role in achieving global greenhouse gas emission targets. However, efficiently operating an electric bus fleet (EBF) requires a comprehensive approach that considers both mobility and energy systems, particularly when implementing opportunity charging strategies. Existing literature and many real-life implementations often focus on only one of these systems, oversimplifying the other, which can lead to inefficiencies, operational challenges, or even unfeasible implementations. To fill this gap, we propose a framework to assess the impact of bus opportunity charging strategies on the power grid by integrating a traffic simulation model (SUMO) and a power grid simulation model (Gaia). SUMO evaluates the energy consumption and charging needs of the EBs, while Gaia assesses the impact of the transformer load in the distribution grid. The integrated method is applied to Rotterdam’s bus line 36 to demonstrate the practicality of this approach. Results indicate that designing an electric bus route with opportunity charging is feasible only when both mobility and energy systems are carefully coordinated.