Development of battery system for railway vehicle

West Japan Railway Company (JR WEST) has been developing battery-powered trains that are intended to improve energy saving for diesel cars in non-electrified sections. In our development, the battery system can be connected directly to the inverter due to its voltage. Simple circuit structure can be expected. We confirmed the possibility of the system by running test. In addition, we carried out thermal simulation and grasped heat characteristics as a next step. In this paper, we introduce the characteristics of our system, the results of running tests and thermal simulation.