A relay holding circuit, comprising: a high-voltage isolated power source, a power source driving module, a first switching device and a microprocessor of a battery management system; wherein the high-voltage isolated power source is respectively connectable to two electrodes of a battery pack, connected to an output terminal of the power source driving module, the microprocessor, and a first terminal of the first switching device; an input terminal of the power source driving module is connected to the microprocessor, a control terminal of the first switching device is connected to the microprocessor, the first terminal of the first switching device is further connectable to a power supply electrode of a lead acid battery, a second terminal of the first switching device is connectable to a coil of a relay, and the relay connects an electrode of the battery pack and a motor; the microprocessor is further connectable to the power supply electrode of the lead acid battery, the microprocessor outputs a low-level signal to the power source driving module when the lead acid battery supplies power abnormally, and the power source driving module enables the high-voltage isolated power source to convert high-voltage power output by the battery pack into low-voltage power in response to the low-level signal, so as to supply power to the microprocessor and the second terminal of the first switching device, such that the coil of the relay remains a conducting state during a period that the lead acid battery supplies power abnormally; wherein the power source driving module comprises: a first switching unit, a second switching unit, and a delay unit; wherein the microprocessor is respectively connected to a first terminal of the first switching unit and a first terminal of the second switching unit, an input terminal of the delay unit is connected to a second terminal of the first switching unit, and an output terminal of the delay unit is respectively connected to the high-voltage isolated power source and a second terminal of the second switching unit; the microprocessor respectively outputs a low-level signal to the first switching unit and the second switching unit when the lead acid battery supplies power abnormally, the first switching unit and the second switching unit are turned off in response to the low-level signal, and the delay unit outputs a high-level signal with delay in a predetermined time period after the first switching unit is turned off, so as to enable the high-voltage isolated power source to supply power to the microprocessor and the second terminal of the first switching device. the high-voltage isolated power source is respectively connectable to two electrodes of a battery pack, connected to an output terminal of the power source driving module, the microprocessor, and a first terminal of the first switching device; an input terminal of the power source driving module is connected to the microprocessor, a control terminal of the first switching device is connected to the microprocessor, the first terminal of the first switching device is further connectable to a power supply electrode of a lead acid battery, a second terminal of the first switching device is connectable to a coil of a relay, and the relay connects an electrode of the battery pack and a motor; the microprocessor is further connectable to the power supply electrode of the lead acid battery, the microprocessor outputs a low-level signal to the power source driving module when the lead acid battery supplies power abnormally, and the power source driving module enables the high-voltage isolated power source to convert high-voltage power output by the battery pack into low-voltage power in response to the low-level signal, so as to supply power to the microprocessor and the second terminal of the first switching device, such that the coil of the relay remains a conducting state during a period that the lead acid battery supplies power abnormally; wherein the power source driving module comprises: a first switching unit, a second switching unit, and a delay unit; wherein the microprocessor is respectively connected to a first terminal of the first switching unit and a first terminal of the second switching unit, an input terminal of the delay unit is connected to a second terminal of the first switching unit, and an output terminal of the delay unit is respectively connected to the high-voltage isolated power source and a second terminal of the second switching unit; the microprocessor respectively outputs a low-level signal to the first switching unit and the second switching unit when the lead acid battery supplies power abnormally, the first switching unit and the second switching unit are turned off in response to the low-level signal, and the delay unit outputs a high-level signal with delay in a predetermined time period after the first switching unit is turned off, so as to enable the high-voltage isolated power source to supply power to the microprocessor and the second terminal of the first switching device.