If you know your battery is shot and you don’t have a way to save your install if the power goes out, then you just don’t update. There are plenty of ways to protect against this that have already been mentioned (battery backup, backup kernel, etc). OP was just playing with fire.

I mean any which way you try to frame this, saying that you won’t use Arch anymore because you didn’t take the precautions necessary based on your situation is gonna take some heat here.