[joosters]

Other devices (e.g. iOS) will warn you if you try to start an update with low battery power, so you can't make this mistake in the first place. Besides, the device itself can spot a low battery (and act on it to ensure the system stays consistent), so why does there need to be a user option to put the device to sleep during the upgrade?

My guess is that Microsoft didn't think about this at all, leading to the rubbish user experience.

[melling]

It doesn't just warn you, it prevents you from making that mistake.