I was tired of replacing the AAA battery in my noise cancelling headphones. This thing replaces the AAA battery and gets power from a USB port on the computer the headphones are connected to. Now i have un-interrupted noise-cancelling and i can forget about the batteries!
Note that this is only practical if your headphone battery compartment is located in-line on the cord.
I didn't include any capacitors because i didn't think they would easily fit inside the battery. i'm not worried about it since USB power is pretty clean, you may want to try to include them.
Pint thing with raft and supports. This is a pretty small object, so infill and resolution don't matter (mine printed in 12 minutes).
Secure the smallest, most flexible USB cable you can find. I used an old cell phone charging cable. cut off the end that doesn't attach to the computer. cut back the cable end so that 2" of the red/black wires are sticking out (cut off the other conductors. you don't need them).
Clean up the print with a hobby knife so that the two halves fit together nicely and the USB cable hole is the correct size. drill two holes in each end with the smallest drill bit you have.
Build the circuit as shown. use pliers so you don't burn your fingers. Visually verify that you don't have any shorts. Plug circuit into a USB port and verify it is producing the correct voltage. (1.8V with no load).
Install circuit into battery. loop solid or tinned wire through the holes in the end of the battery and attach to circuit. Verify a second time that you have no shorts and that it is producing the correct voltage.
Super glue everything together. I found that twist ties worked well to hold the two halves together while the glue dries.