A portable power supply adapted to be connected to an external power source and to an electronic device comprises a main module comprising a battery, a satellite module comprising an input port, and output port, and an interface panel, and a tether cable, and a controller. The controller a first mode to allow the battery to be charged when the external power supply is connected to the input port, a second mode to allow power to be supplied to the electronic device from the battery when the electronic device is connected to the output port, and a third mode to allow the battery to be charged and power to be supplied to the electronic device when the external power supply is connected to the input port and the electronic device is connected to the output port.