QMax learning/updates do not occur until the GaugingStatus()[QEN] flag is set by sending the Gauging() (0x0021) command to AltManufacturerAccess().
The following conditions will prevent a QMax update when an OCV is taken.
TemperatureIf Temperature() is outside of the range 10°C to 40°C
Delta CapacityIf the capacity change between suitable battery rest periods is less than 37%
VoltageIf Voltage() is inside a flat voltage region. (See the Support of Multiple Li-Ion Chemistries with Impedance Track Gas Gauges Application Report (SLUA372) for the voltage ranges of other chemistries.) This flat region varies with different chemistries. The GaugingStatus()[OCVFR] flag indicates if the cell voltage is inside this flat region when GaugingStatus()[REST] is set. Prior to an exit from CHARGE or DISCHARGE mode, the GaugingStatus()[QMAXDODOK] flag can be checked to determine if the cell is in the flat zone.
Offset ErrorIf the offset error accumulated during the time passed from the previous OCV reading exceeds 1.5% of Design Capacity mAh, the update is disqualified. Offset error current is calculated as a function of Coulomb Counter Deadband and the sense resistor value. For applications with small battery capacities, an offset error of 1.5% of Design Capacity mAh can be reached in a short period of time, especially with a small sense resistor. Therefore, a minimum time of 11 hours from the last qualified OCV is enforced before disqualification, which facilitates QMax updates in such applications. Enforcing this minimum time can increase an offset error to as high as 5.5% of Design Capacity mAh.