Electric power tool arrangement comprising an electric power tool comprising - a housing, - an electric motor located inside the housing, - a working element protruding from the housing, - wherein the electric motor is connected to the working element in order to impose a rotational and/or an eccentric working movement (130, 132) to the working element, and - two or more battery units (36, 44) adapted to provide electric energy to the electric motor for its operation, wherein one of the battery units is an external battery unit provided separately from the rest of the electric power tool and releasably attachable and electrically connectable to the rest of the electric power tool, wherein the at least one other battery unit is an internal battery unit fixedly located inside the housing and electrically connected to the rest of the electric power tool, wherein the electric power tool arrangement further comprises a voltage converter unit provided separately from the rest of the electric power tool and releasably attachable and electrically connectable to the rest of the electric power tool in place of the external battery unit, the voltage converter unit being adapted to be connected to a mains power supply and to convert a mains voltage provided by the mains power supply to a voltage of the at least one internal battery unit, and characterized in that after attachment and electric contacting of the voltage converter unit to the rest of the electric power tool the voltage converter unit is adapted to exclusively provide electric energy to the electric motor for its operation while the at least one internal battery unit provides no electric energy to the electric motor. - a housing, - an electric motor located inside the housing, - a working element protruding from the housing, - wherein the electric motor is connected to the working element in order to impose a rotational and/or an eccentric working movement (130, 132) to the working element, and - two or more battery units (36, 44) adapted to provide electric energy to the electric motor for its operation, wherein one of the battery units is an external battery unit provided separately from the rest of the electric power tool and releasably attachable and electrically connectable to the rest of the electric power tool, wherein the at least one other battery unit is an internal battery unit fixedly located inside the housing and electrically connected to the rest of the electric power tool, wherein the electric power tool arrangement further comprises a voltage converter unit provided separately from the rest of the electric power tool and releasably attachable and electrically connectable to the rest of the electric power tool in place of the external battery unit, the voltage converter unit being adapted to be connected to a mains power supply and to convert a mains voltage provided by the mains power supply to a voltage of the at least one internal battery unit, and characterized in that after attachment and electric contacting of the voltage converter unit to the rest of the electric power tool the voltage converter unit is adapted to exclusively provide electric energy to the electric motor for its operation while the at least one internal battery unit provides no electric energy to the electric motor.