And, of course, once I post, I find one listing for this light under the UltraFire name. When I search for the model number, I find a review here of an XHP50 version from 2015
Unfortunately, the reviewer had trouble getting the head apart. The bezel ring doesn’t offer easy purchase, and taking the retaining screws out of the opposite end didn’t not free the driver board.
I expect that the parallel configuration of cells makes the charging feature much simpler to implement.
I wonder how hard it would be to set this host up for 3s (forgoing the charging). It sounds like there isn’t enough room for protected cells, which is itself a problem, and also suggests there isn’t room for a board at the head-end. Maybe some room could be picked up at the tail end, depending on how close the tail PCB is to the tailcap already. Also, thinner contact rings at the head-end could help. Or, put the needed contacts on the driver board, and make the light load from the tail.