The invention concerns a portable power supply system (30) intended to supply a remotely controlled, electrically driven work machine (1) with electrical power, where the work machine is of the type that demonstrates a propulsion means that includes continuous tracks (8b) and is equipped with a maneuverable arm (10) intended to carry a tool at its free end, and electric motor (19) that is connected to a hydraulic pump (20) and is intended to supply the operating means (8c, 10a) of the machine with a hydraulic medium, whereby the work machine is intended to be connected under normal operation to a primary source of power (30a) via an electrical cable (2′), which primary source of power includes a fixed alternating current electricity distribution grid at the location. In order to be able to supply the current that is required it comprises a DC energy-storage arrangement (29) that, including a secondary source of power (30b), can store energy and, when necessary, supply energy in electrical form; a coupling arrangement (31, 33, 34, 34′) that makes it possible to choose between connecting the primary (30a) or the secondary (30b) source of power to the electric motor in order to drive the same.