I have a nice Maglite ML125, which is designed to take a 6V NiMH battery pack (5x small cells) or 3 C alkalines. Sadly, the battery pack is toast, and replacements are really expensive.
Now, I could get a single cell Li-Ion adapter, but that’s not going to be very impressive. What I was thinking is something like this:
Obviously, I’d only use protected cells in this. Would that high (8.4V peak, 7.4V average) of voltage cook the driver / LED?
My guess is, it would probably be too much voltage for the driver and fry it. Try searching to see if others have tried to mod this light with 2 x lithium cells for 8.4V.
You could also try 2 x 26700 LiFePO4 Cells, which charge to 3.4V for a total of 6.8V. Then make your own spacer. You’ll need a charger capable of charging LiFePO4 cells, which many of the cylindrical cell chargers we use have that capability.
Use a couple of these and maybe some tiny magnets if you need a button top.
I was looking at those cells - would the lack of protection be a problem for running them in series? Would a 26500 be too tight a squeeze?