The invention relates, among other things, to an electrical energy source (100; 100') for an electrically drivable tool (200), containing: a main body (101; 101'), which extends along a longitudinal axis (L; L'), having a first end (102; 102') and a second end (103; 103') lying opposite the first end (102; 102') with respect to the longitudinal axis (L; L'); at least one first electrical terminal (104; 104'), which extends away from the first end (102; 102') and has a first diameter (d1; d