A portable electronic system equipped with a spare battery device. The portable electronic system includes a spare battery device and a portable device. The spare battery device includes a first fixer unit, a power storage unit and a sensory control unit. The sensory control unit further includes a constant voltage source, a resistor, a resilient object, output contact pads, and a control unit. The portable device includes a second fixer unit, a covering, and input contact pads. By adjusting the coupling relationship between the first fixer unit and the second fixer unit, each output contact pad can be coupled to the associated input contact pads; and the control unit is for controlling output power of the spare battery device.