One of the other issues with the standard coulomb-counting gauge method is that it is necessary to do a full charge or discharge cycle to learn the full capacity of the battery. This gives two reference points between which the total charge passed that can represent the Qmax value. However if the battery is really fully discharged, the system will shut off and won’t be able to store the data values that it’s just learned. So, two reference values corresponding to 3% and 7% are used as calibration points. These values must be characterized for each battery type in the lab before using the gauge in a product design. So, while coulomb counting can add a degree of accuracy to the simple voltage based measurement, it also has some issues with providing a highly accurate estimate in practice.