The Nikon EN-EL12 battery is used to power Nikon's Coolpix and KeyMission cameras. I kept running out of charge when I was doing photomicrography so I wanted to connect the camera to a wall adapter, but the official adapter (EH-62F) costs AU$90 which is too rich for my blood.

This is a battery shell that has a cut-out to allow you to insert the controller board from an EN-EL12 battery (or a third-party clone of one) and connect that to external power.

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0.2 mm

15 %

• Soldering equipment (soldering iron, solder, solder wick, sponges, heat shrink, side cutters, etc.)
• A sacrifical EN-EL12 battery or a third-party clone. I used a third-party battery marked "Seiwei battery pack for EN-EL12" that had continuity between the positive and negative poles and was therefore internally ruined.
• An AC adapter. My camera (Coolpix P330) wants a power source of 3.7–4.2 V at 1.1–1.2 A, but I did not have an adapter that fell within that low voltage range with that kind of amperage. The closest I could find was a 5.0 V 1.2 A adapter. The camera seems to be okay with this, but it's possible that overvolting the camera could reduce its component life. I will try to source a more appropriate AC adapter online.
• Thin wire. I used stuff from a telephone wire.
• Connectors between the battery and the AC adapter. My adapter fit a barrel jack with terminal blocks, so I used that. You could also just solder the wires together.

1. Print EN-EL12 external power.stl. I've also included the .f3d file so that you can open it in Fusion 360 if you need to make changes. The design is fully parametric.
2. Remove the outer cover of the sacrificial battery to expose the innards. Cut the controller board free. Dispose of the lithium battery responsibly (they can explode/catch fire).
3. Clean up the B+ and B- terminals and solder new wires to them.
4. Install the board inside the shell. You will need to file about 1 mm off the length of the board to make it fit (because I had to make sure that the walls had adequate thickness). Pay attention to how the battery terminals align with the cutouts on the shell, and remove material from the board in a way that helps that alignment.
5. Run the wires through the through the cut-outs in the shell.
6. Use heat shrink to add strain relief to the wires where they would exit the camera.
7. Connect the controller board's wires to the AC adapter, B+ to positive and B- to negative. Install the shell in the camera and see if the camera turns on. If it does not, try pushing the shell hard into the battery compartment to make sure it's making contact. If you need to do this, then it means that your shell printed too short, and you'll need to put some soft foam at the battery door to keep it pressed down.
8. If everything works, wrap the shell in thin sticky tape to keep it all together.

2018-08-18

• Initial upload.