We needed to power up a piece of surveillance equipment, but it took C cell batteries and all the ones we had were dead. So using the Swiss army knife that is the 3D printer, we made some nice adapters that allow you to insert AA batteries into any device that's designed to accept C cells! The voltage is the same, so no worries there, but certain high-current devices might not like the higher equivalent series resistance (ESR) of the AA versus the C cell. For low-current applications, this should do just fine. Two versions of the adapter are included. The first version, upon printing, was discovered to be a bit too snug around the AA. This may vary by 3D printer and materials, so we're including it anyway. We still managed to get the AA in there with a few taps from a hammer. The second version is 0.2mm wider on the internal diameter, so it did not require any hammering to get the AA in. We suggest printing version 2, and if the AA fits too loosely inside of it, try version 1. Have fun! ~ PeterPrinted successfully on a 3D Systems Cube in neon green PLA.