A battery pack, comprising: a first battery terminal and a second battery terminal; a plurality of battery units, each said battery unit comprising; a battery cell; a cell supervisor electrically connected to the battery cell, the cell supervisor comprising a set of registers put in series; and a communication section configured to communicate with the cell supervisor, the communication section comprising a data buffer; wherein all of said battery cells are connected serially between the first battery terminal and the second battery terminal; a plurality of bus interfaces (109a, 109b, 109c) arranged in alternating fashion with said battery units to define a daisy chain bus, each said bus interface (109a, 109b, 109c) configured for signal communication, each said bus interface (109a, 109b, 109c) respectively connecting the communication sections of two adjacent said battery units; and a battery manager configured to communicate with said battery units via the daisy chain bus, wherein the battery pack is configured so that the battery manager sends a command message to the battery units using a through mode protocol, and each said battery unit sends at least one of a confirmation message and a service request to the battery manager using a shift mode protocol, wherein in the through mode protocol, data is transferred via the data buffer, while in the shift mode protocol, data is shifted along the set of registers. a first battery terminal and a second battery terminal; a plurality of battery units, each said battery unit comprising; a battery cell; a cell supervisor electrically connected to the battery cell, the cell supervisor comprising a set of registers put in series; and a communication section configured to communicate with the cell supervisor, the communication section comprising a data buffer; wherein all of said battery cells are connected serially between the first battery terminal and the second battery terminal; a battery cell; a cell supervisor electrically connected to the battery cell, the cell supervisor comprising a set of registers put in series; and a communication section configured to communicate with the cell supervisor, the communication section comprising a data buffer; wherein all of said battery cells are connected serially between the first battery terminal and the second battery terminal; a plurality of bus interfaces (109a, 109b, 109c) arranged in alternating fashion with said battery units to define a daisy chain bus, each said bus interface (109a, 109b, 109c) configured for signal communication, each said bus interface (109a, 109b, 109c) respectively connecting the communication sections of two adjacent said battery units; and a battery manager configured to communicate with said battery units via the daisy chain bus, wherein the battery pack is configured so that the battery manager sends a command message to the battery units using a through mode protocol, and each said battery unit sends at least one of a confirmation message and a service request to the battery manager using a shift mode protocol, wherein in the through mode protocol, data is transferred via the data buffer, while in the shift mode protocol, data is shifted along the set of registers.