The utility model provides a power system, comprising a battery module, a control module and a distribution box, wherein the power module is connected with the control module which is connected with the distribution box. The battery module is composed of at least two series modules; each series module is formed by the series connection of at least two battery sets. The control module comprises a relay module, a relay control module and an IGBT module, wherein the relay module is composed of a number of relays; the series module is connected with the relay module which is connected with the IGBT module; the relay control module controls the on-off of the relay in the relay module and selects each series module to combine with the IGBT module. The control module combines the battery set in the battery module via the relay module and controls the battery set via the relay control module, so that the battery set is heated in groups and the voltage between the battery sets is balanced.