This is real MacGyver territory. I've been stuck in a handful of urban survival situations and the inevitably dying phone battery is by far one of the more pressing issues. Most important will of course be immediate safety, shelter, water and food, etc., but it's likely that the use of a phone will help you secure those things. And when the power is knocked out it can be a real challenge.
So here you are: How to Charge Your Phone with a 9-Volt Battery. All you need is a battery, a key, a car charger, and preferably some duct tape and you'll be all set. Check out the video below, try it out for yourself and let us know your results!