A system for controlling a battery to extend a driving mileage is provided. The system supplies a high voltage required to drive a motor by connecting a plurality of batteries in series by turning off a battery switching unit during engaged of an accelerator and balances voltage between the plurality of batteries. A voltage deviation is managed by connecting the plurality of batteries in parallel by turning on the battery switching unit when the accelerator is disengaged. The system includes a plurality of battery modules and a battery switching unit configured to connect the plurality of battery modules in parallel when an accelerator is disengaged and connect the plurality of battery modules in series when the accelerator is engaged. A motor driving unit is configured to receive an output by the battery switching unit when the accelerator is engaged.