In case it wasn't obvious, my ambition to revive some old NiCad C batteries is more for curiosity than any practical reason. Yes, replacement would cost a few bucks, but hardly breaking the bank. In fact the C cell battery holders I bought to help charge them cost about half the cost of the battery cell, so I definitely can't hide behind cost saving as an excuse.

Buying replacements isn't the only thing we can try, either. I was amused when I learned that battery size adapters existed. Apparently, modern NiMH rechargeable batteries in AA form factor can meet electrical demands that formerly required C or D cell alkaline batteries, so it's possible to put those NiMH AA cells into a sleeve that helps them fit into space designed for C or D cells.

Far from an unauthorized use or hack, such adapters are occasionally bundled along with batteries as seen at my neighborhood Costco. This pack of Energizer branded NiMH rechargeable cells are bundled with four AA to C adapters, and four AA to D adapters.

Inconveniently (or possibly simply a result of Murphy's Law) Emily's printer takes five batteries, and there are only four adapters of each size. This is irritating not just because of the current project, but that there are six AA NiMH batteries in this package. Thus they did not include enough adapters to use all six AA batteries.... nor would six batteries be enough to fill all eight adapters. It's the hot dog & hot dog bun packaging issue all over again, except this mismatch is in the same package!

Back to the adapters: D-cell adapters have a physical electrical connection, as D cells are slightly longer than AA batteries. However, C cells are roughly the same length, so the AA to C adapter is a passive plastic sleeve with a hollow center and no electrical connection. This makes me think we can 3D print a few for experiment's sake. And as Randy Glenn commented on yesterday's entry, people have already uploaded adapters to Thingiverse, and modified versions thereof, to help people do exactly that.