bq20z65RSOC Drift

We have a 4S1P (Chem ID 1104) pack that uses a bq20z65 fuel gauge. As the pack cycles up and down The RSOC begins to drift upwards. By the 10^th or 12^th cycle the RSOC reads approx. 26% at full discharge.

What can be done to correct the RSOC so that it does not drift upwards through the life of the pack?

The customer requirement is for the pack to be able to cycle between 16.8 volts at full charge, to 12v at full discharge.

Thanks.