for the G6, the tip will not illuminate once it's fully charged and the LED on the charger is solid blue. When you unplug it, it will blink 3 times, thats normal.
I know the book reads you gotta charge it for 8 hours, but in reality, these batteries are almost fully charged when you get them.
The G6 is a little wonky, as the battery fades, the LED may start to dim as you inhale through it, eventually it will blink indicating it is at a critically low level. That's when you want to recharge it back to full. Lithium Ion batteries lives are determined by the number of times they charge, not really for how long. Each should be good for 300-ish charging sessions.
to add, unless the battery is blinking when you try to vape, it's good to go. Use it and throw the cigs away, or give them to someone you dont like, like my Step-Mom's sister that refuses to use enough butter in her mashed potatoes.