Have you ever wanted to use an AC adapter on something that wasn't designed for one? This makes it easier. After a simple wire wrap for a connector, this fits in a AAA battery compartment and makes contact with either the positive or negative terminal simply by being the same size as a battery. If your gadget has 6 batteries, you can just print 2 of these and place the contacts on the end connections.

Print the short piece with the open end up, and make sure to use a brim on the long piece - supports not needed.