An octet of Eneloop AAA cells arrived, I wanted to measure their as-delivered charge (the package says “Factory Charged With SOLAR ENERGY”, so you know it’s good), and discovered I’d given away my AAA cell holders. You can actually get inter-series adapters on eBay, but what’s the fun in that? Plus, I didn’t want to delay gratification for a month; you know how it is.

Soooo:

AAA to AA Adapter – top – Slic3r

It’s basically an AA-size sleeve that fits over the AAA cell, with a lathe-turned brass post conducting juice from the + terminal of the inner cell outward:

AAA to AA Adapter – parts

Not much to look at when it’s assembled:

AAA to AA Adapter – assembled

The AAA cell fits deliberately loose, because this goes into a metal clip holding everything firmly in place for the battery tester:

AAA to AA Adapter – in use

The source code tabulates the sizes of several cylindrical cells, exactly zero other pairs of which have been tested; I expect most won’t work correctly. In particular, the table entries should include the contact button OD and thickness for each cell, so that I can turn out the proper terminal for each pair of cells. If I ever need a different adapter, I’ll beat some cooperation out of that, too.

Discovered I needed an adapter after breakfast, started testing cells after lunch. Life is good!

The OpenSCAD source code as a GitHub Gist:

The original doodle:

AAA to AA Adapter – sketch