A battery monitoring system includes a carbon dioxide sensing system configured to selectively measure carbon dioxide concentrations within a plurality of battery cells, respectively, that are connected in parallel. A controller is configured to detect cathode overpotential in the plurality of battery cells in response to the measured carbon dioxide concentrations of the plurality of battery cells.

Provided is a battery module and battery rack having enhanced fire safety features. The battery module includes an applied pressure assembly with integrated sensor that detects swelling of a battery cell. An output signal of the sensor is used to halt operation of a battery system containing the battery module and an output signal of the sensor is used to halt charging and discharging of the battery module. In an embodiment, the battery module uses an AC-to-AC power supply to provide audio frequency power for balancing battery cells of the battery module. In an embodiment, the battery rack includes a directed water fire suppression system that provides battery cooling after a fire to ensure the fire does not reignite.