Battery system

A sensor board receives a voltage difference between a battery pack not connected to the power bus and the power bus; determines whether the voltage difference indicates that a battery pack voltage is within a threshold voltage difference from a power bus voltage; in response to determining the voltage difference indicates that the battery pack voltage is not within the threshold voltage difference from the power bus voltage, provides a drain indication to drain off the battery pack using a power draw mechanism until the voltage of the battery pack is within a threshold voltage difference of the power bus; and provides a connect indication to connect the disconnected battery pack to the power bus.