Small sustainable electronics are an important part of the emerging fields of IoT, sensing, and exploration. Our project is a Solar charging subsystem. The project will focus on developing a solar charging system that is as low cost and energy efficient as possible as 2W solar recharging. The design needs to be small, contain its own battery, and have an ability to turn off its output based on an enable signal that when it is disabled.Our design requires two different systems: low and high current designs. Low current design allows current up to 100mA and high current design allows current up to 5A.Some key technologies implemented in this project are: a solar charging circuit and a coulomb counter that provides current-flow, voltage, and temperature measurement data to support battery capacity monitoring in cost-sensitive applications. Also, a standard I2C Interface with software programmable address that gives the controlling microprocessor access to all data and status register inside the IC chip. One accomplishment is our coulomb counter which accurately displays the remaining amp hours. Some challenges were the implementation of the coulomb counter and the communication via the I2C protocol.