This paper presents a solar charger ASIC for Nickelbased (NiCd or NiMH) batteries. The system is fully integrated and no external component is needed. The ASIC includes a voltage reference, a low-impedance switch, an oscillator, a poweron reset, and a digital control block. The circuit is fabricated in a fully digital 0.35μm 3.3V process. It features a low power consumption of 10μA and operates with a low power supply voltage in the 0.6V to 1.5V range.