I had my phone in that insulated bag in an inner jacket pocket, and it was dead after Oracle. Glad I didn't need it to find my way home or call for help. Next time- BGY technique.
You should patent them- call it an i-warmer and charge a premium.
PS- if you use only one you can wrap the second air-tight in cling wrap and it won't turn on until you unwrap it.
Your technical prowess impresses once again...