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

Some circuits are designed to only feed off the battery. So even when plugged in all the circuits rely on the one battery feed. This is a hardware design choice, but not one to be taken lightly. Allowing both external power and battery power runs the risk of the user removing the external power with no battery reserves. This can cause irreversible data loss. Apple devises for example feed off both, but when you plug a dead apple devise into the wall it won’t power on right away. The software requires a margin of error so the battery has enough for a safe power down.