State-of-Charge Measurement for Lithium-Ion Batteries is an advanced task, but can be simplified using specific ICs able to measure accurate SOC of Li-Ion batteries. Stephen Evanczuk writes:
All energy-harvesting-based systems need energy storage for times when the energy cannot be harvested (e.g., at night for solar-powered systems). Rechargeable batteries ‒ known as “secondary” cells to differentiate them from “primary” or single-use cells ‒ are usually specified for this task.
For rechargeable batteries, however, battery management depends on the best possible measurement of what is known as the state-of-charge (SOC) of battery cells. For lithium-ion batteries, the characteristics of Li-ion cells complicate SOC measurement and can challenge engineers looking to maximize Li-ion battery lifetime. To simplify design of Li-ion battery management systems, engineers can leverage a variety of SOC measurement techniques supported in ICs from Atmel, Linear Technology, Maxim Integrated Products, STMicroelectronics, and Texas Instruments.
Advanced ICs Simplify Accurate State-of-Charge Measurement for Lithium-Ion Batteries – [Link]