A reconfigurable energy storage system comprising: one or more energy modules comprising: a plurality of circuits interconnected to each other, each circuit having at least two input/output terminals, which can function as input or output terminals, and an energy storage unit with a positive terminal and a negative terminal, either of which can be interposed between the input/output terminals; the plurality of circuits including a switch module having 2n + 2 switches, where n is 1 or more and is based upon the number of energy storage units connected between the two input/output terminals and where the switch module provides series, and/or bypass connectivity for and enables the ability to reverse polarity in said energy storage unit; and a control unit that is adapted to monitor an operational state of the energy storage unit in the energy modules and to control the switches, to bypass, connect the energy storage unit in series, and/or change the polarity of said energy storage unit when connected with the plurality of circuits in accordance with the operational state, wherein the control unit is further adapted to determine a number of energy storage units available for use from the energy storage units in the plurality of circuits; characterised in that the or each output terminal of the n th circuit is connected to the or each corresponding input terminal of the (n+1) th circuit, at least one of the 2n + 2 switches is disposed between the energy storage unit of the n th circuit and the energy storage unit of the (n+1) th circuit, and in use, at least half of the 2n + 2 switches must be closed for current to pass through the plurality of circuits. a plurality of circuits interconnected to each other, each circuit having at least two input/output terminals, which can function as input or output terminals, and an energy storage unit with a positive terminal and a negative terminal, either of which can be interposed between the input/output terminals; the plurality of circuits including a switch module having 2n + 2 switches, where n is 1 or more and is based upon the number of energy storage units connected between the two input/output terminals and where the switch module provides series, and/or bypass connectivity for and enables the ability to reverse polarity in said energy storage unit; and a control unit that is adapted to monitor an operational state of the energy storage unit in the energy modules and to control the switches, to bypass, connect the energy storage unit in series, and/or change the polarity of said energy storage unit when connected with the plurality of circuits in accordance with the operational state, wherein the control unit is further adapted to determine a number of energy storage units available for use from the energy storage units in the plurality of circuits; characterised in that the or each output terminal of the n th circuit is connected to the or each corresponding input terminal of the (n+1) th circuit, at least one of the 2n + 2 switches is disposed between the energy storage unit of the n th circuit and the energy storage unit of the (n+1) th circuit, and in use, at least half of the 2n + 2 switches must be closed for current to pass through the plurality of circuits.