An energy storage module includes a module housing, a positive polarity module terminal and a negative polarity module terminal accessible via an external surface of the housing, and a plurality of battery cells contained within the housing and coupled in series between the positive polarity terminal and a negative polarity terminal to form a battery cell string. A removable manual service disconnect (MSD) unit is physically coupled to the external surface of the housing and electrically coupled between at least one battery cell in the battery cell string and one of the module terminals. The MSD unit has at least a first MSD operating state to allow current conduction between the positive polarity module terminal and the negative polarity module terminal, and a second MSD operating state to prevent current conduction between the positive polarity module terminal and the negative polarity module terminal.