A portable system includes a portable device and a power adapter to supply power to the portable device. The portable device includes a rechargeable battery and a measurement chip to measure charge remaining in the rechargeable battery. The power adapter includes a transmission line, a microprocessor, and a display unit. The microprocessor receives the readout of the amount of charge remaining in the rechargeable battery from the measurement chip via the transmission line, and generates a display signal according to the charge remaining. The display unit displays the charging progress of the rechargeable battery according to the display signal received from the microprocessor.