What is the electrical reason some devices like mobile phones require a working battery even during times when they are plugged into a wall?

Question

If the battery fails on a mobile phone, why is it unusable even when it’s plugged in to the wall?
There are many older electrical gadgets that can work with either batteries or being plugged in. Take an old fashioned alarm clock or stereo. If there’s no batteries in it, and you plug it into the wall it will work. If you unplug it, it won’t work unless there are good batteries in it that are charged. So why can’t a mobile phone work when plugged into the wall when the battery has failed?

In: 18

Answer 1

I dunno about phones, but I have worked on several things that don’t get their power from an external source in any fashion. They pull power directly from the battery and the battery pulls its power from the external source. Could just be the way it’s wired internally.