Does anyone make a smart phone battery charger that operates on 6 Volt DC input?

Mark

There are 6-12v step ups made that you can connect to any interface you like. I have one connected to a cigarette lighter that I run my GPS with.

Our cell phone 12 volt charger plugs into the 6 volt socket and charges the phone.

USB (phones)or Micro USB (GPS) ports provide 5volts DC to the device for charging. So like Chipper has found, as long as you can make the physical connection from the 6volts of the car, most of the adapters should work...

I read that after I'd already installed mine. If the step up ever fails I'll just wire direct to 6v.

Your step up might be needed with some devices due the varying "quality" of some of the electronics...