A non-aqueous electrolyte battery system includes a battery voltage output section for outputting a voltage of a non-aqueous electrolyte secondary battery and a freezing determination section for performing freezing determination to a non-aqueous electrolyte. In the freezing determination, the freezing determination section executes freezing determination current control for supplying a current at a freezing determination current value at a freezing determination time in a direction to charge the non-aqueous electrolyte secondary battery. When a voltage value output from the battery voltage output section exhibits a transition that rises once to a peak value during execution of the freezing determination current control, and then decreases with time, it is determined that the non-aqueous electrolyte is in a frozen state.