very easy USB 9 volt charger
Step 1: parts list
L78M05CV 5V 500 Ma voltage regulator
9 volt battery snap
USB connector (female) ,or phone charger plug
of course soldering iron and some solder.
optional - extra wire ,heat shrink ,recharge able 9v battery ,multimeter (for checking if all are working correctly.)
I bought 9v 250 Mah battery for 6$. I think if you build this you'll need recharge able battery. For wire i just use wire from 9v battery snap.