RSTC is resistor value drift with temperature. You can find this characteristic value from your RTC datasheet. The DS2788 is factory programmed with the sense resistor temperature coefficient, RSTC, set to zero, which turns off the temperature compensation function. RSTC is user accessible and can be reprogrammed after module or pack manufacture to improve the current accuracy when using a high temperature coefficient current-sense resistor. More information can be found in the Sense Resistor Temperature Compensation paragraph in the DS2788 datasheet.