The difference in power draw between idle and 100% utilization on a modern computer is enormous.
The power adapter needs to be able to handle 100%, but the sort of usage where you get 6-12 hours of use while on battery is very much near idle almost all the time.
I have a 15" MacBook Pro, which has a 95Wh battery. Apple claims 8 hours of battery life on it, and in my experience that's an understatement. It also ships with an 85W power adapter.
> The power adapter needs to be able to handle 100%
Actually it can't; there used to be a support article on Apple's site named HT2332 that details how Macbooks will underclock with the battery removed, because the adapter cannot supply enough power with the system at full load. Other manufacturer's laptops have also been doing this, so Apple is not alone.
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.
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.
The power adapter needs to be able to handle 100%, but the sort of usage where you get 6-12 hours of use while on battery is very much near idle almost all the time.
I have a 15" MacBook Pro, which has a 95Wh battery. Apple claims 8 hours of battery life on it, and in my experience that's an understatement. It also ships with an 85W power adapter.