Battery Full [Q] Charging while powered down

I've never understood how the screen works while charging, while the phone is off. Is this some sort of system partition, or low powered mode? The reason why I ask, is whenever I try and charge it, the screen stays on, along with the LED Notification light. It never changes, and thus, I can never tell when it's 'fully' charged.

Any help? Is there a way to fix this by flashing something? I feel weird having my screen on all night trying to charge my phone.

Also, I forgot to mention, I can't turn it on, while it's off and charging. If I try to, it seems to freeze, and the only way to turn it on, is to disconnect, and hold the power button until it reboots. Have I messed up something crucial?