A method for a battery system for a vehicle is provided. The battery system can include a plurality of battery modules and a heat transfer assembly. Each of the battery modules can include one or more cells. The battery modules are selectively electrically connectable to a terminal of the battery system in order to provide electrical power to the vehicle. The heat transfer assembly can selectively adjust thermal energy levels of one or more of the battery modules. The method can include determining a desired capacity of the battery system, determining a number of the battery modules to have thermal energy levels adjusted by the heat transfer assembly according to the desired capacity of the battery system, and operating the heat transfer assembly to adjust thermal energy levels of the determined number of battery modules.