I have the same issue on my new G5 5587. It is definitely power throttling when it is on battery and not plugged in. When it is on power everything is working fine. No matter what settings I tweak, I am unable to change that. I am not talking while gaming only. Even whilst doing nothing and the temperatures are around 50 degrees immediately when I unplug the power the power limit throttling is enabled and the max core frequency drops more than 70% that ruins even my windows experience....(just by pressing on the windows home button I can see some jittering). Here are some pictures that were taken from Intel Extreme Tuning Utility to prove what I am saying.
While plugged in :
This is unacceptable for a newly bought gaming laptop as I can't even browse the internet on battery....