Battery pack for an electric or hybrid vehicle comprising an electric power supply system, that comprises: a power source having first and second poles (2,3), 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 (2,3), 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.