© 2020 IEEE.Most of the DC fast chargers have 50-150 kW power rates in the market. These power rates may give a suitable charging time for personal EVs but not for commercial electric vehicles. Thus, the DC fast charger should be improved to charge bigger battery capacities in an acceptable charging time. Especially, the regular DC fast chargers cannot give acceptable charging time for the electric buses and/or electric heavy trucks. The new battery and power electronic technology make it possible to use much more power rate for fast charging. These high-power rate chargers are called ultra-fast charging and/or extremely fast charging. In this study, the ultra-fast charging system has been used to reduce the charging time of public buses. The updated charger standards such as CHAdeMO and SAE have been taken into consideration. Accordingly, the 450 kW ultra-fast charging system is used for on-route charging to analyze the battery size of the electric bus. In addition, the benefit of having an on-route charging station has been evaluated and compared with having no charging station in terminals. Public bus routes have been used to optimize bus battery capacity according to the bus schedule, stop time, and the ultra-fast charger power limit. The optimum battery size is calculated and optimum route length has been proposed for a given scenario for the E-buses.