You can leave your Gamepad to charge when not using it?

I just need this answering because it seems as though the battery life drains pretty quickly. I can leave it to charge whilst I am watching TV or other things.

Yeah. I leave mine plugged in all the time. No issues. You can also buy an extended life battery if you want. Supposedly the Nintendo first party battery gives you 8 hours on 1 charge.

Yes, the Gamepad dies quick. My setup wouldn't allow it to be kept plugged in at all times in the livingroom, but it does charge when you aren't playing on it.

You have two options. Leave it plugged in directly when not using it, or just use the charging cradle that it comes with. You can just set it down and it will charge and then grab it when you want to game.

I just leave it on the cradle when i'm not using it...

This.