Not that it's a justification, per se, but a lot of modern laptops won't boot without a battery. The power adapter often can't provide sufficient power to spin everything up at boot, and needs the battery as a buffer (this is why, if you run your macbook battery completely flat, it needs to charge for a few minutes before it can boot back up).
They can't boot without a battery, but for a different reason: The laptop only draws power from the battery, not from the power plug. There is no power connection other than through the battery.
Why are laptops being sold with insufficient power adapters then? That also sounds just flat wrong. Most non-gaming laptops have power supplies with significantly higher outputs than their maximum power draw, and the boot-up surge is incredibly tiny. I would be flatly amazed if a MacBook boot up power draw was even 10% higher than system power draw under maximum load.
MacBooks in particular use USB-C for power these days, which is currently capped at delivering 100 watts. By comparison, many gaming laptops over in the Windows side of the world ship with 180-230 watt power adaptors (using proprietary connectors).
Perhaps among other reasons, folks don't want to carry a giant adapter around with their laptop. I've seen adapters for "engineering" laptops, that seemed as big as my entire laptop.
Considering that the battery in a MacBook is non-removable, it's not just a corner case - it's a warranty-voiding act that the designers explicitly don't have to account for.
Well I literally powered up an oldish laptop two days ago that had been sitting there for a few years, and it turned off three times within a few seconds of booting until I let it sit for a few minutes for the battery to charge.
The power brick is rated at 19V 3.16A output, so 60W, the CPU is a 35W TDP second-gen i3.
Of course a big part of that is spinning up the disk, so as you say I imagine this is quite different these days with SSDs.
> I've not come across any laptop or Android smartphone that wouldn't power up without a battery.
I had the pleasure of working on an Android smartphone that wouldn't power up without a battery. Or even with a battery, if the outside temperatures were sufficiently low to cause the battery voltage to drop below the FCC-defined limits for running the radios.
