I have the model GX531GW.
If you tear down the laptop to the point where you have removed the keyboard panel, the cmos battery can be seen on the top side of the motherboard.
It is under a piece of felt electrical tape on my model.
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It is located on the lh side of the laptop, just at the base of the motherboard where it meets the battery.
It is about 3cm to the right of a white ribbon cable which is for the left hand side USB board