A portable self-contained electric power tool unit, includes at least three distinct sub-assemblies. The tool is characterised in that the second sub-assembly (3) may be carried by the user and includes a lithium-ion or lithium-polymer electrochemical battery (5) formed by combination of more than four cells (6) in series, each cell being made of one or several elements in parallel and a control and operating module (7) for the battery (5), guaranteeing a maximum battery capacity over time in a controlled manner and an optimal use of the tool. The first sub-assembly (2), during operation thereof, is subject to control by a current-limiting system (8), for preserving the lithium-ion or lithium-polymer battery (5) from which the above draws energy and the third sub-assembly (4) has at least one source of electrical supply, the voltage and current of which are suitable for the recharging of the lithium-ion or lithium-polymer battery (5).