Zandparts has 3rd party batteries forG751. They emailed me this link.
https://www.zandparts.com/en/Zand%20Parts-ZPCS-AUG751NBFor whats its worth I had all problems described above with my G751JT. For years I muddled through until battery pack went completely dead.
I mustered up courage and bought a new battery off Amazon, found the utube video where the guys replaces battery on G751. I followed his steps and I now have a fresh battery and its like a new computer to me. No more worries about all the flashing lights.
BTW I took the old battery pack apart to see if any of the 18561 batteries were good. I tested them all and though old and low on capacity they were all still good and probably were not the cause of failure. I attribute failure of this pack to the BMS, battery management system board that is in the pack, which controls the charging and balance of the 8 / 18650 LIPo batteries. These circuit boards are the weakness IMHO.