Are there any viable 32mm cells for a 3D cell maglight? I’m expecting to do at least a 2S setup.
I don’t know how common they are, but there are 32650 cells.
I think the bigger problem is that Li-Ion cells are higher voltage than D cells, but I’m not an expert on the matter. 
I plan on doing a modded mag, I need higher volts anyway. Plan to do LED, but I might do a hotwire for !@#$ and giggles.
I would love to piggy back on any substantial mods.
I keep a 30 year old 3D Mag in my car with a cheapie LED retrofit drop in from Home Depot. Love to show it more love.
There are half a dozen options to power a maglite, li ions,32800, 32650, 26650, 21700, 18650, 3.2v and 3.7v chemistry, protected and not. For hotwire you need high current cells with no protection circuit. preferably imr or inr chemistry for 3.7v or lifepo4 for 3.2v cells,
Led mods usually do not draw as much so protected cells will work.
What I’m more looking for is what cell sizes are economical in terms of Ah/$, what cells have good power density, and what cells haven’t really progressed in a decade? I’ve been out of the loop for a bit due to work and school demolishing my free time and I’m not sure what cells have been given decent R&D love and what cells give marginal benefit. My last light I bought was from 2016, the BLF A6. Gave it some high quality cells for that sweet sweet direct drive turbo.
The problem is that I don’t know what’s decent these days so I figured I field the question while I dig through data to catch up (I’m an electrical engineer, this ain’t my first rodeo)
I’m considering doing a 3S liion (or lifep04 if my girlfriend is worried about my safety) setup unprotected with a driver with low voltage lockout because any cell dropping to close to 0V will make the overall pack volts drop enough that there’s no way it’ll hit that in normal use.
Being curious I bought a 3D and a 6D on Marktplaats.nl (Dutch version of the likes of Craigslist). And a few (not that cheapy) retrofit bulb replacements. I noticed that the business end of a Maglite is totally made of plastic, so you have to do some extensive modding to create a sufficient heat-path before you worry about cell’s with enough staying power.
I have a friend with a lathe that can turn metal. The old standard a decade+ ago was to use a drop in of correct size, but there’s much to be said for hammering a metal slug into the light.