A system for balancing a plurality of battery pack system modules (202a, b, c, d) connected in series, the system comprising: a plurality of battery pack system modules (202a, b, c, d) connected in series, wherein a high charge module of the plurality of battery pack system modules (202a, b, c, d) has a charge greater than a charge for other modules of the plurality of battery pack system modules connected in series, characterised in that each of the battery pack system modules (202a, b, c, d) comprises a controller assembly, at least one disconnect circuit that has a charge switch, and at least one balancing circuit (25a, 25b), wherein the controller assembly is adapted to actuate the charge switch of the at least one disconnect circuit when the battery pack system module (202a, b, c, d) reaches a predetermined state of charge selected to prolong the life of the battery pack system modules (202a, b, c, d), and to balance the state of charge of the battery pack system module (202a, b, c, d) with that of other battery pack system modules (202a, b, c, d) by partially discharging the battery pack system module (202a, b, c, d) when the battery pack system module (202a, b, c, d) reaches the predetermined state of charge; at least one Zener diode connected in series with a current limiting resistor, wherein the at least one Zener diode is in communication with the at least one disconnect circuit of at least one of the plurality of battery pack system modules (202a, b, c, d); and a power source connected to the at least one disconnect circuit, wherein current from the power source is limited by the current limiting resistor, and wherein the at least one Zener diode enables current from the power source to bypass at least one of the plurality of battery pack system modules (202a, b, c, d) at the predetermined state of charge to charge at least one other battery pack system module (202a, b, c, d). a plurality of battery pack system modules (202a, b, c, d) connected in series, wherein a high charge module of the plurality of battery pack system modules (202a, b, c, d) has a charge greater than a charge for other modules of the plurality of battery pack system modules connected in series, characterised in that each of the battery pack system modules (202a, b, c, d) comprises a controller assembly, at least one disconnect circuit that has a charge switch, and at least one balancing circuit (25a, 25b), wherein the controller assembly is adapted to actuate the charge switch of the at least one disconnect circuit when the battery pack system module (202a, b, c, d) reaches a predetermined state of charge selected to prolong the life of the battery pack system modules (202a, b, c, d), and to balance the state of charge of the battery pack system module (202a, b, c, d) with that of other battery pack system modules (202a, b, c, d) by partially discharging the battery pack system module (202a, b, c, d) when the battery pack system module (202a, b, c, d) reaches the predetermined state of charge; at least one Zener diode connected in series with a current limiting resistor, wherein the at least one Zener diode is in communication with the at least one disconnect circuit of at least one of the plurality of battery pack system modules (202a, b, c, d); and a power source connected to the at least one disconnect circuit, wherein current from the power source is limited by the current limiting resistor, and wherein the at least one Zener diode enables current from the power source to bypass at least one of the plurality of battery pack system modules (202a, b, c, d) at the predetermined state of charge to charge at least one other battery pack system module (202a, b, c, d).