Who is responsible for checking/ blocking a laptop from booting due to low battery? Motherboard's POST, bootloader or the kernel?

Question

is it the motherboard's post that will prevent a critically low battery from continuing with booting up the OS?

is it the bootloader's responsibility? (e.x GRUB)

or is it the kernel who runs some hardware checks that prevents it?

thanks!

Answer 1

That entirely depends on at what stage the power will run out.

• The POST is the most demanding operation as regarding power consumption. If the juice runs out during POST, the device will just shut down. Typically, the fans will start up and just stop.
• After POST, if the boot loader doesn't detect a power source and if it considers that the battery is too low to boot into the firmware, it will shut down the device.
• When the OS kernel is loaded, it will boot or not according to its parameters. It may also decide after boot to shutdown whenever power is critically low.

Answer 2

The earliest stage would probably be battery's built in discharge protection circuit which will cut off power to prevent discharging below a threshold where charging the battery again could cause fire.

The motherboard should refuse to boot before reaching levels that low though.