Power supply unit which is designed and intended for supplying at least one hydraulic drive motor of a heavy-duty vehicle (10; 10') with hydraulic fluid by means of a drive-hydraulic line system of the heavy-duty vehicle (10; 10'), comprising: - a hydraulic pump that can be driven by an associated electric motor and is designed and intended for conveying hydraulic fluid to the drive-hydraulic line system of the heavy-duty vehicle (10; 10') during operation, characterised in that the power supply unit further comprises: - a frame to which the hydraulic pump is fastened, comprising first connecting elements which are designed and intended for interacting with first mating connecting elements of the heavy-duty vehicle (10; 10') in order to operatively rigidly mechanically connect the power supply unit to the heavy-duty vehicle (10; 10'), and comprising second connecting elements which are designed and intended for interacting with second mating connecting elements of a further functional unit (18; 118) in order to be able to operatively rigidly mechanically connect the power supply unit to a further functional unit (18; 118), and - a battery pack which is fastened to the frame and is designed and intended for supplying the electric motor with electrical driving power, the hydraulic pump and the electric motor being designed such that the hydraulic pump can be operated as a hydraulic motor and the electric motor can be operated as an electric generator. - a hydraulic pump that can be driven by an associated electric motor and is designed and intended for conveying hydraulic fluid to the drive-hydraulic line system of the heavy-duty vehicle (10; 10') during operation, - a frame to which the hydraulic pump is fastened, comprising first connecting elements which are designed and intended for interacting with first mating connecting elements of the heavy-duty vehicle (10; 10') in order to operatively rigidly mechanically connect the power supply unit to the heavy-duty vehicle (10; 10'), and comprising second connecting elements which are designed and intended for interacting with second mating connecting elements of a further functional unit (18; 118) in order to be able to operatively rigidly mechanically connect the power supply unit to a further functional unit (18; 118), and comprising first connecting elements which are designed and intended for interacting with first mating connecting elements of the heavy-duty vehicle (10; 10') in order to operatively rigidly mechanically connect the power supply unit to the heavy-duty vehicle (10; 10'), and comprising second connecting elements which are designed and intended for interacting with second mating connecting elements of a further functional unit (18; 118) in order to be able to operatively rigidly mechanically connect the power supply unit to a further functional unit (18; 118), and - a battery pack which is fastened to the frame and is designed and intended for supplying the electric motor with electrical driving power, the hydraulic pump and the electric motor being designed such that the hydraulic pump can be operated as a hydraulic motor and the electric motor can be operated as an electric generator.