I’ve made a very simple portable USB charger, using a 9V battery as a power supply. I’m using this to charge my MicroTrack when I’m in a middle of a field recording and power runs out.
I’ve used a 7805 voltage regulator IC, 2 pieces of 0.1uF electrolytic capacitors, a switch, battery holder, USB A connector, heat sink for the regulator, some wires and a plastic box. You can view the schematics here.
UPDATE: Mozso noticed me that two 100 nF ceramic capacitors are needed too. I’ve updated the schematics.
I don’t know how long the battery will last, but I’ll write about it. Unfortunately, (9V-5V)*500mA = 2 watts are dissipated through the heatsink.