Refer below quoted text from Page 27 of SLUSAW3C bq40z60 datasheet.
"If the average discharge current is high, the system can turn ON the CHG FET for improved efficiency and minimized line losses during the discharge phase."
This statement is wrong. CHG FET is N-channel MOSFET. It can not allow current to flow in reverse direction. The discharge current will flow from diode of CHG FET and DSG FET only.