Battery pack for an electric or hybrid vehicle comprising an electric power supply system, that comprises: a power source having first and second poles , a circuit breaker device connected at the first pole for alternatively breaking and enabling circulation of current there-through, a switch device connected at the second pole , a control module operatively associated with the circuit breaker device and with the switch device for controlling their operation to alternatively connect and disconnect the power source , wherein the control module is adapted for sequentially opening and closing the circuit breaker device and the switch device , such that the control module opens or closes the switch device only when no current is flowing through the circuit breaker device , wherein the control module is adapted such that, for connecting the power source to supply electric power, the control module closes the switch device before closing the circuit breaker device , wherein the control module is also adapted such that, for interrupting the supply of electric power, the control module opens the circuit breaker device before opening the switch device , and wherein the switch device has a power switching capability lower than the circuit breaker device capability, characterized in that the switch device is only connected at the second pole and to one pole of a load , and further comprising current detecting means for detecting current flowing through the switch device , and wherein the current detecting means are in communication with the control module , and the control module is also adapted for controlling the circuit breaker device and/or the switch device as a function of a signal received from the current detecting means , to assure that the switch device is ordered to transit to its open or closed state only when no current is flowing through the battery . a power source having first and second poles , a circuit breaker device connected at the first pole for alternatively breaking and enabling circulation of current there-through, a switch device connected at the second pole , a control module operatively associated with the circuit breaker device and with the switch device for controlling their operation to alternatively connect and disconnect the power source , wherein the control module is adapted for sequentially opening and closing the circuit breaker device and the switch device , such that the control module opens or closes the switch device only when no current is flowing through the circuit breaker device , wherein the control module is adapted such that, for connecting the power source to supply electric power, the control module closes the switch device before closing the circuit breaker device , wherein the control module is also adapted such that, for interrupting the supply of electric power, the control module opens the circuit breaker device before opening the switch device , and wherein the switch device has a power switching capability lower than the circuit breaker device capability, characterized in that the switch device is only connected at the second pole and to one pole of a load , and further comprising current detecting means for detecting current flowing through the switch device , and wherein the current detecting means are in communication with the control module , and the control module is also adapted for controlling the circuit breaker device and/or the switch device as a function of a signal received from the current detecting means , to assure that the switch device is ordered to transit to its open or closed state only when no current is flowing through the battery . <EOS>