Abstract: An automatic charging system for charging nickel-metal-hydride batteries is presented. The battery charging system uses a method of detecting the lowest charge current to control its charging process. The system has a constant voltage power supply including a short-circuit protection device, a battery voltage detector, a current detector, a current to voltage converter, a voltage amplifier, an analog to digital converter, a single chip microcomputer, a capacity indicator, a time indicator and a full-charge indicator. The system uses a constant voltage to charge batteries with a floating current according to the quantity of the active ions in the batteries. The battery charge current is converted to a voltage signal which is then amplified and digitized. The microcomputer detects the digitized signal to estimate the magnitude of the charge current.