I don't have the 680 manual, but the AC6 manual, next to the last page (pg 36) lists the charge and discharge current for 1S thru 6S lipo batts.

The AC6 is 50watts so this wouldn't apply to the 680 (80watts), but check toward the end of your 680 manual and see if it doesn't have the same listing, just for your 80watt charger.