A battery monitoring system includes a data acquiring unit and a failure determining unit. The data acquiring unit acquires a plurality of types of monitoring data to monitor a state of a secondary battery. The failure determining unit determines whether the secondary battery has failed. The failure determining unit performs sparsity regularization using the monitoring data as variables and calculates a partial correlation coefficient matrix of the monitoring data. The failure determining unit calculates, as an abnormality level, an amount of change in a partial correlation coefficient, which is a component of the partial correlation coefficient matrix, between two partial correlation coefficient matrices calculated at different periods. The failure determining unit determines that the secondary battery has failed when the calculated abnormality level exceeds a predetermined threshold.