A server includes an enclosure, a motherboard, a number of hard disk drives (HDDs), a number of built-in batteries, and a server power module. The motherboard includes a power management interface and a base management controller. When the server power module works normally, the server power module outputs a voltage to the motherboard to power the motherboard, and charge the built-in batteries. When the server power module cannot work normally, the built-in batteries output voltages to the motherboard to keep the motherboard working, while the base management controller stores data of the server to the HDDs and powers off the motherboard.