The USB adapter itself will draw enough current to ruin your following day. Ensure the whole thing is unplugged when you've finished, not just the USB device.

I've got a USB socket that's wired into the taillight wire under my seat, and mounted under the front, by the coil. That way it comes on when the ignition/accessories are on but when I switch the bike off, there's no chance of me leaving it to drain the battery.

 

that's what i'm saying though. the one i posted won't. it has a cutoff that makes sure you will always have enough battery to start your bike.

 

I am looking to do a bar mounted version for cellphone, GPS and GoPro camera

 

Search for this on Amazon. EKLIPES EK1-110 Chrome Cobra Ultimate Motorcycle USB Charging System

I have put this system on two different bikes now and have had zero issues with it. For $24 you can't go wrong. It has a port for a cigarette charger socket and a usb port and mounts to the handle bars. I have a dual usb charger in the cigarette socket and I keep two ecigs plugged in to that and my cell phone or gps in the usb port. It has never drained the battery and has worked everytime I needed it.