Making Stuff: Improvised C-Cell Batteries

I get a sense of satisfaction, usually far out of proportion with the actual accomplishment, when I manage to achieve some minor technical win in day-to-day life.  One recent example was the creation of improvised C-cell batteries.

We have a Sony shower radio that requires four C-cell batteries, which need to be replaced about every 10 months under normal daily use.  It is, I think, the only device in our house that uses C-Cell batteries anymore.  I end up needing to buy batteries specifically for it every time it needs new batteries.  This last time the batteries died, however, I decided to take advantage of the fact that C cells are the same length as AA, of which we have plenty.  And yes, I know that there are plastic shells into which you can slide a AA battery to make it C-size.  But the same result can ALSO be achieved with strips of cardboard (in this case, cut from 12-pack Coke boxes) wrapped around the battery to achieve the proper outer diameter, and then duct-taped in place.

This is what the finished adapted battery looks like:

And here's the set of four installed in the radio battery compartment:

So, what are the limitations of this approach?  Well, obviously the pseudo-C battery only has the capacity of a AA.  If you look at many rechargeable batteries, however, you will find that the C-cells you can buy often have exactly the same storage capacity as the same brand's AA batteries.  In other words, they are just putting AA cells into C-sized packages.  The reduced capacity battery will only last about half as long as "real" C-cells, but then I can just untape them, unwind the strip of cardboard, and replace the AA at the core.

The peak current sourcing capacity of the AA battery is also less than a C-cell, but unless you're drawing really high current (and this radio just doesn't) this is not a limitation.  Likewise, in applications that draw extremely high currents, the batteries may actually heat up enough due to their heightened internal resistance that cardboard duct-taped around the AA becomes a hazard.  But again, this "transistor radio" application doesn't come anywhere near that level of current draw.

When working on home projects, I often have to decide up front that the amusement value of making something work is far more valuable than the actual fix.  Was it worth the time to measure, cut, roll, and tape cardboard to build adapters when I could have just grabbed the batteries the next time I was at virtually any store?  Of course not!  Did it amuse me, and offer the satisfaction of a hack done entirely with materials I had on hand?   Absolutely!