A power tool comprising: an electrical motor unit that is connectable to a battery unit; - a step-up converter that is connectable between said battery unit and said electrical motor unit, which is arranged for converting, when enabled, a battery voltage U battery that is provided to said step-up converter by said battery unit to a higher step-up voltage U step-up; U step-up > U battery; said step-up voltage U step-up being provided to said electrical motor unit as an output voltage U output; U output =U step-up; - a bypass circuit that is arranged in parallel with said step-up converter and connects, when enabled, said battery unit to said electrical motor unit and provides said battery voltage U battery to said electrical motor unit as an output voltage U output; U output =U battery; and - at least one control unit (331, 332) that is arranged for controlling said step-up converter and said bypass circuit such that said output voltage U output may be switched between said battery voltage U battery and said step-up voltage U step-up, characterised in that the control unit (331, 332) is arranged to control the step-up converter and said bypass circuit based on a number of different parameters, taken alone or in combination, which parameters comprise the output voltage U output, an output current I output being provided to said motor, a rotational speed ω motor of said motor unit multiplied with a torque T being provided by said tool; ω motor *T, and an output power P output being provided to said electrical motor unit. an electrical motor unit that is connectable to a battery unit; - a step-up converter that is connectable between said battery unit and said electrical motor unit, which is arranged for converting, when enabled, a battery voltage U battery that is provided to said step-up converter by said battery unit to a higher step-up voltage U step-up; U step-up > U battery; said step-up voltage U step-up being provided to said electrical motor unit as an output voltage U output; U output =U step-up; - a bypass circuit that is arranged in parallel with said step-up converter and connects, when enabled, said battery unit to said electrical motor unit and provides said battery voltage U battery to said electrical motor unit as an output voltage U output; U output =U battery; and - at least one control unit (331, 332) that is arranged for controlling said step-up converter and said bypass circuit such that said output voltage U output may be switched between said battery voltage U battery and said step-up voltage U step-up, characterised in that the control unit (331, 332) is arranged to control the step-up converter and said bypass circuit based on a number of different parameters, taken alone or in combination, which parameters comprise the output voltage U output, an output current I output being provided to said motor, a rotational speed ω motor of said motor unit multiplied with a torque T being provided by said tool; ω motor *T, and an output power P output being provided to said electrical motor unit. - a step-up converter that is connectable between said battery unit and said electrical motor unit, which is arranged for converting, when enabled, a battery voltage U battery that is provided to said step-up converter by said battery unit to a higher step-up voltage U step-up; U step-up > U battery; said step-up voltage U step-up being provided to said electrical motor unit as an output voltage U output; U output =U step-up; - a bypass circuit that is arranged in parallel with said step-up converter and connects, when enabled, said battery unit to said electrical motor unit and provides said battery voltage U battery to said electrical motor unit as an output voltage U output; U output =U battery; and - at least one control unit (331, 332) that is arranged for controlling said step-up converter and said bypass circuit such that said output voltage U output may be switched between said battery voltage U battery and said step-up voltage U step-up, characterised in that the control unit (331, 332) is arranged to control the step-up converter and said bypass circuit based on a number of different parameters, taken alone or in combination, which parameters comprise the output voltage U output, an output current I output being provided to said motor, a rotational speed ω motor of said motor unit multiplied with a torque T being provided by said tool; ω motor *T, and an output power P output being provided to said electrical motor unit.