How to rig up cell phone charge when car is off?

[BennyLava]

Hi all. I want to rig my 2009 Yaris sedan to still be able to charge my cell phone when the key is out of the ignition. Right now, when you take the key out, it cuts power to the power points (aka cigarette lighters) in the car.

How can I make those things still have power when the key is out? I often would like to just leave my phone charging while I go do something, when I'm out in town or at work. My Ford car and my Chevy truck both allow you to charge when the key is not in the ignition. But my yaris won't. I assume that I just need to replace a relay, or merge a fuse somewhere?