Hey there,
By any chance, does anyone here knows of reasonable-priced 2x 26650 -> 3 C adapters?
I have looked for them everywhere, but apart from ordering custom-made ones at prices that are incompatible with my wallet thickness, I have not found any… 
Do you mean a spacer?
I think a spacer will accomplish what they are asking for, but isn’t what they are currently envisioning.
So, you need a 2cm piece of something conductive with a diameter of 25 or 26mm.
You can use anything you can drill a hole through when you give it a conductive core (some copper wire for example).
Yep, I need a spacer!
The issue with DYIing is that I currently live far from home in a rented apartment and I have no tools or any modding equipment here. So I’d rather buy a pre-made thing.
I see.
Maybe you can get a piece of metal (aluminium will be cheapest and lightest) with those sizes from a local vendor?
Put a layer of tape around it and presto! 
That sounds like my best option… But how can I make piece of aluminium in button-top form factor? 
I have bunch of those tiny neodymium magnets, can they be soldered?
O right, hadn’t thought about the teat yet…
Maybe the magnets can be soldered, not sure, but I think they’re usually nickel plated.
But you can not solder (the normal way) aluminium…
But probably the magnet sticks to the 18650 minus pole.
Go to a hardware store and look around. Find something round that’s the right diameter like a large fiber washer, and stick a nut and bolt (or something through the middle).
Probably not a very elegant approach. But you can get AA to C cell adapters (Eneloop do one I think). And you can get dummy AA cell spacers from places like FastTech.
So put the AA dummy cell in the C cell and adapter and hey presto a dummy C cell.
That's too long, only needs ~4-15mm., depending. Protected cells are longer and fatter.
Did you check fit? Most 26650's are too large in diameter for a lot of C cell tubes.
He needs 20mm when he uses 2x unprotected flat top 26650.
C cells are 50mm tall
Here’s the battery tray in question (sorry, crappy cellphone pic). It takes 8x C normally (so 8-12V), but rechargeable C’s are too expensive, and I’d need a new charger.
Figured I could use 4x 26650 in there (which would give me 10-14V, device works normally at those voltages), as I have a lot of A123Systems ANR26650M1A cells lying around… Just got to figure out how to, uhh, fill the void.
It’s 20mm indeed.
Since your batteries are surrounded by plastic, all you need is a ball of tinfoil to fill in the gap.
Aha, I was thinking tube, flashlight, a 3x C-cell Mag or so…
In the lower left corner of the picture there’s that contact plate to put the cells in series.
It (most probably) has no wire attached, so you can take it out and move it to the right, glue a piece of wood in between that plate and where that plate used to be, and you have it fit.
…but then it will not take C-cells anymore…
Tin foil could work too, I guess… :bigsmile:
What kind of a device is it? I believe that your A123 cells are unprotected, so be careful not to overdischarge them…
It’s a oooold as hell (20+ yrs) FM stereo that I have heavily modded internally to match modern ages.
Found it like this:
Ripped out insides, cleaned it from dust, dirt etc
Added speakers back
…and then I also added Yamaha YDA148-powered amplifier board, but sadly I have forgot to take a photo after doing it.
I also plan to add mini 3-17V voltmeter, already ordered it, so I am not going to suffer from over-discharge.
Batteries, basically, are the only thing left to figure out. :3
What I also had in mind was building a huge 3.7V pack (e.g. 10 18650’s in parallel) and adding charging controller and DC-DC boost converter to feed the amplifier, but that requires money, and I don’t have much at the moment. So re-using A123 cells that I already have seemed the most sensible thing to do.