I have the G751JY and when it is charging there's an orange light and when it is fully charged it turns green ( should be the same for you too ). As soon as this light turns green you must unplug the charger from the PC because ( this happens to all the devices with rechargable batteries ) if the PC stays plugged in after it is fully charged that will constantly over time reduce the battery's life time and duration when it is unplugged until it eventually ( this happened to my cousin, he had his laptop plugged in every single second, day and night, night and day ) as soon as you unplug it in 5 min the battery has been drained and needs to be recharged. The only solution if that happens is to buy a new battery. Also when you are not using your PC unplug the charger from the power socket as well just to be safe.
