the answer is yes, this has been addressed many times this G series notebooks under heavy load will use power from your battery as well as your power adapter. If you remove the power adapter your CPU and GPU will automatically throttle down. So yes to play games you need both the power supply connected and battery.
G752VY-DH72 Win 10 Pro
512 GB M.2 Samsung 960 Pro
1 TB Samsung 850 pro 2.5 format
980m GTX 4 GB
32GB DDR 4 Standard RAM
Z97 PRO WiFi I7 4790K
Windows 10 Pro
Z97 -A
Windows 10 Pro