Re: Mains powered phones?
I'm going to hate myself for saying this (and possibly defending Apple) - I'm no battery or electronics expert, but my understanding is even when charging, phones are powered by the battery, and the mains current adds to the battery as it's inputting more than the battery is outputting.
If the battery is struggling to output enough power, it may not make a difference how much power is being input to it at the time.
You can see the inverse of this on Samsung tablets: charge it off a PC USB 1/2 port while using it, and the battery icon will have a red X through it, indicating that although it has external power, it's not getting more than the battery is outputting so the battery is draining, albeit more slowly. If it had switched directly to the USB input, it wouldn't have enough power and would fail.
Happy to be corrected by someone who does know what they're talking about. :)