An electrical energy source for an electrically drivable tool, in particular an electrically drivable surgical tool, in particular an electrically drivable surgical screwdriver, comprising - a housing that in particular, at least partly, forms a main body of the energy source, - at least one voltage source, arranged in the housing, for generating an electrical voltage, - at least one second terminal, and - at least one inner electrical contact, wherein the voltage generated by the voltage source is applied or can be applied between the second terminal and the inner electrical contact; which comprises at least one electrical contact element having a first electrical contact and a second electrical contact that are electrically connected to each other, wherein - the contact element comprises a first terminal, which comprises the second contact; - the contact element is in a standby position, in which it is releasably connected, directly or indirectly, to the housing, and in which neither the first contact nor the second contact is electrically connected to the inner contact; - by action of a force that can be exerted by a first tap-off element of the tool, the contact element can be moved from the standby position into an operating position in which the first contact is electrically connected to the inner contact, such that the voltage generated by the voltage source is applied between the second terminal and the first tap-off element; - after the first tap-off element has been removed for the first time, the contact element moves from the operating position into an end position in which the contact element can no longer be brought into electrical contact with the first tap-off element, such that the voltage generated by the voltage source can no longer be applied between the second terminal and the first tap-off element. - a housing that in particular, at least partly, forms a main body of the energy source, - at least one voltage source, arranged in the housing, for generating an electrical voltage, - at least one second terminal, and - at least one inner electrical contact, wherein the voltage generated by the voltage source is applied or can be applied between the second terminal and the inner electrical contact; which comprises at least one electrical contact element having a first electrical contact and a second electrical contact that are electrically connected to each other, wherein - the contact element comprises a first terminal, which comprises the second contact; - the contact element is in a standby position, in which it is releasably connected, directly or indirectly, to the housing, and in which neither the first contact nor the second contact is electrically connected to the inner contact; - by action of a force that can be exerted by a first tap-off element of the tool, the contact element can be moved from the standby position into an operating position in which the first contact is electrically connected to the inner contact, such that the voltage generated by the voltage source is applied between the second terminal and the first tap-off element; - after the first tap-off element has been removed for the first time, the contact element moves from the operating position into an end position in which the contact element can no longer be brought into electrical contact with the first tap-off element, such that the voltage generated by the voltage source can no longer be applied between the second terminal and the first tap-off element.