An electrical energy supply apparatus comprising: a main body (1-I, 1-II, 1-III); multiple cells disposed in the main body (1-I, 1-II, 1-III), where a product of a nominal voltage of each cell and a quantity of the cells is greater than or equal to 60 V; an electrical energy output device (9-I, 61-II, 30-III) comprising a flexible connection apparatus, where an input end of the flexible connection apparatus is electrically connected to the cells, an electrical energy output interface (91-I, 65-II, 37-III) is disposed at an output end of the flexible connection apparatus and the electrical energy output interface (91-I, 65-II, 37-III) is connectable to an external power tool (50-I, 100-II, 200-III) to supply electrical energy to the external power tool (50-I, 100-II, 200-III); and a conversion circuit, converting a voltage of a cell into an output voltage of the electrical energy output interface (91-I, 65-II, 37-III), where when the conversion circuit is in a first state, the electrical energy output interface (91-I, 65-II, 37-III) outputs a first voltage, when the conversion circuit is in a second state, the electrical energy output interface outputs a second voltage, and the first voltage is less than the second voltage; the cells form at least two standard battery units; the conversion circuit comprising a series-parallel circuit including a switch device, wherein a quantity of the switch devices is less than a quantity of the standard battery units by one, wherein the switch device is disposed between two adjoined standard battery units, each switch device including two relays, separately forming the first subswitch and the second subswitch, wherein the first subswitch and the second subswitch are linked via an optical coupler, wherein when the first subswitch is turned on, the optical coupler is triggered to enable the second subswitch to be turned on. a main body (1-I, 1-II, 1-III); multiple cells disposed in the main body (1-I, 1-II, 1-III), where a product of a nominal voltage of each cell and a quantity of the cells is greater than or equal to 60 V; an electrical energy output device (9-I, 61-II, 30-III) comprising a flexible connection apparatus, where an input end of the flexible connection apparatus is electrically connected to the cells, an electrical energy output interface (91-I, 65-II, 37-III) is disposed at an output end of the flexible connection apparatus and the electrical energy output interface (91-I, 65-II, 37-III) is connectable to an external power tool (50-I, 100-II, 200-III) to supply electrical energy to the external power tool (50-I, 100-II, 200-III); and a conversion circuit, converting a voltage of a cell into an output voltage of the electrical energy output interface (91-I, 65-II, 37-III), where when the conversion circuit is in a first state, the electrical energy output interface (91-I, 65-II, 37-III) outputs a first voltage, when the conversion circuit is in a second state, the electrical energy output interface outputs a second voltage, and the first voltage is less than the second voltage; the cells form at least two standard battery units; the conversion circuit comprising a series-parallel circuit including a switch device, wherein a quantity of the switch devices is less than a quantity of the standard battery units by one, wherein the switch device is disposed between two adjoined standard battery units, each switch device including two relays, separately forming the first subswitch and the second subswitch, wherein the first subswitch and the second subswitch are linked via an optical coupler, wherein when the first subswitch is turned on, the optical coupler is triggered to enable the second subswitch to be turned on.