Provided is a battery module and battery rack having enhanced fire safety features. The battery module includes a swelling/pressure sensor that detects swelling of a battery cell. An output signal of the sensor is used to halt operation of a battery rack/battery system containing the battery module and prevent charging and discharging of the battery module. In an embodiment, the battery module uses an AC-to-AC power supply to provide AC frequency power for balancing battery cells of the battery module. In an embodiment, the battery rack includes an internal water fire suppression system that provides battery cooling in the event of a battery cell fire to prevent the spread and/or reigniting of the fire.