I'm coming here to comment because, as we speak, I have my laptop charging behind me and am waiting for it to reach 100% so I can put it away. I have to keep checking it manually. Right now I'd love if it just made a bloop sound back there so I didn't have to think about it.
However, when I'm actually using my laptop, I wouldn't want it to send a notification. If anything, an OSD or an icon animation like Méven describes would be the way to go I think.
I wouldn't mind a noise and notification by default if the screen is off/locked or asleep. Not sure how feasible that is to implement though, and not sure how users would figure out what the random sound meant.