Our paper evaluates the energy consumption and battery performance of city transit electric buses operating on real day-to-day routes and standardized bus drive cycles, based on a developed framework tool that links bus electrification feasibility with real-world vehicle performance, city transit bus service reliability, battery sizing and charging infrastructure. The impacts of battery capacity combined with regular and ultrafast charging over different routes have been analyzed in terms of the ability to maintain city transit bus service reliability like conventional buses. These results show that ultrafast charging via frequent short-time boost charging events, for example at a designated bus stop after completing each circuit of an assigned route, can play a significant role in reducing the battery size and can eliminate the need for longer duration charging events that would cause schedule delays. Furthermore, the analysis presented shows that significant benefits can be realized by employing multiple battery configurations and flexible battery swapping practices in electric buses. These flexible design and use options will allow electric buses to service routes of varying city driving patterns and can therefore enable meaningful reductions to the cost of the vehicle and battery while ensuring service that is as reliable as conventional buses.