This slide shows an example of some reference data for the same type of Li-Ion cell from five different cell manufacturers. The top graph shows the OCV readings versus state of charge, and it is apparent that for a given cell type, the results are nearly identical. So, this data can be used to correlate between a measured OCV and its corresponding state of charge. The graphs on the bottom are zoomed-in showing the variation in voltage and percent error across the state of charge. The error is typically less than one percent. This data is generated for each new type of cell. TI maintains a library of this data for all known Li-Ion and some other cell types, and new types are added as they become available. When designing a gauge circuit for a specific battery type, the reference data for that battery is programmed into the gauge as a “Chemical ID table” in the device’s non-volatile memory.