[mikeash]

That's true, I'm able to drain my MacBook's battery while plugged in if I stress it enough. It's pretty close, though!

I don't suppose you have any idea exactly how they arrive at the power adapter size for these things? It seems to be almost but not quite 100%, but they still try to optimize it where they ship 45W, 65W, or 85W depending on what computer you have.

[userbinator]

At least for the Macs I think it's more to do with how fast it can charge the battery while the system is (mostly) idle or off. A larger adapter is inconvenient, but so is a slow-charging battery.