I build this using
A USB car charger
Half a used laptop battery
Step 1: Building It
Use a screw driver to pop open the plastic housing.
Find a box that the 3 batteries fit in snuggly. If you have a 3D printer printing a housing would work great.
Connect the 3 batteries in series to get 12 Volts total. I also used hot glue to glue the batteries together.
Solder the wires and switch together. The switch disconnects the USB board when not in use. I also soldered wire pieces before the switch so you can charge it with the switch off.
I glued the batteries in the box. I cut holes for the switch, USB plug and charge wires. I glued a piece of cardboard on the end to close the box.
I also added hot glue on the LED which lights up the clear glue.