There was talk earlier about Powerbank cases for Android.
I think this would go 1 better...
A battery belt/(or not) pouch.
I carryy my phone in a belt pouch. Instead of a rucksack/backpack use a belt pouch. As far as I know, no one.else does it.
So imagine... ANY PHONE that can be charged on the go, while still available n handy. The battery is built in, and so it the cable/lead as a retractable (retractable part built into the pouch).
Phone charging, phone rings, remove from pouch with Powerbank still attached via retractable lead. As you place back in pouch, lead withdraws into pouch at same time.
No more, battery n phone in.pocket charging and getting tangled, no more hunting via back pack n disconnecting lead to answer the phone.
I paid retail, but I can get belt pouches for between £5-£10 (GBP) Including postage.