I agree with you on the fact that the spring is already so compressed it could break if dropped pretty hard, I have never broke one, so I don’t know how hard it would have to drop. Given the fact that almost all lights only have one spring in the tail cap, I cant see much difference besides the tail cap spring being tightly compressed but then again, its that way in almost all single cell lights with the longer protected cell inserted.
Come on, once again?
Xiaozhi/D4 from FF/CNQG, fits protected batteries no problem.
Fiddling with switch only helps you to minimize length but won’t help you with battery length, it does not use threads as contact 
Convoy S6 is a copy that has several changes.
On my samples, the body+head length is longer on S6 by 1.3mm.
Where is the culprit?
The reflector depth.
D4: 16.6mm
S6: 18.7mm, with outer 19.9mm.
So S6 reflector is longer by at least 2mm. Also the pill is maybe longer but the driver does not go as deep into the pill.
This all adds up and shaves off some what, maybe 3mm or more of battery length.
Is it a problem? I don’t think so, you just won’t be ale to to screw the head on as much as with D4 or unprotected batteries.
Reducing driver spring length works, but it’s really the reflector and pill that are different on S6 that steal the space.
Not sure all S6 come with the same though. This is what I got from FT S6 host aka sold as XPower host, but ships as Convoy S6.
They have this reflector:
FT Convoy reflector.
Length 19.9mm, diameter 20.4mm.
This one is the same, just more expensive.
As a replacement I only see 20mm by 13 and 15.5mm reflectors for an XP-G. They should work, but the XM-L reflectors are probably gone already. Or they don’t list/sell them. FT nor CNQG.
The D4 reflector has no grooves on the sides, is shorter and bottom is flat with a bump around the reflector hole.
Other replacements, a TIR optic
Which can lead to triples and chopping off 1.5-2cm from the total length while still fitting a protected battery.
BTW I don’t use any ring on the switch but hot glue. Tail screws all the way instead of creating a 1mm gap with the body.
And as you may have noticed, a lot of Convoy Sx lights on FT are listed as UNPROTECTED batteries ONLY.
Adjust pill, reflector, driver, the only place to save a couple millimeters.
Once you get the driver set like you want it, you could also conformal coat it with a few layers of clear nail polish to prevent it shorting
No, I meant with the stock spring it's pretty well protected, removing the spring and replacing it with a solid blob of solder makes it much more fragile. Even a really stiff short spring is more compressible than solder.
I thought everyone knew this ..
the s6 is tight and the s2 demands protected or longer cells
If you take the plastic retaining ring off the S2 and the little brass button and use just the spring (Or solder the button to the spring, what I did = slightly more reliable) then it will fit unprotected cells. I don’t know why they include that washer other than giving you the option of having the brass button.
I don’t really know any ways of making a small host fit bigger cells though, sorry. My M2 still will fit protected cells, but tightly.
I looked around and I could not seem to figure out if the Nanjg 105C actually has low voltage cut-off, or if it just flashes a warning. That is of interest to me because I only use unprotected cells in single cell devices which are mainly my Spark headlamps that do have low voltage cut off, but I have a bunch of flashlights with the QLite and Nanjg 105C that I use, and assumed until now that they had it as well.
Most will do a step-down, then eventually shut off. It depends on the firmware though.
Easy enough to simply pull out a multimeter, turn them on, watch what happens, and measure the results then. THanks.
My point was most drivers don’t have a spring or a solder blob, just the board and battery contact traces on the bottom like the original amc7135 AK-47. We only had a spring in the tail cap back then and used them that way for years. The Nanjg 105 came out with the spring and 8-amc7135’s after a lot of people where stacking bare amc7135 1400ma boards to AK-47 boards with one extra amc7135 on the AK-47 so that they could have modes and a 8-amc7135 2800ma driver. No springs used back then. And there still not used on most drivers. I don’t see the difference if the spring was removed or shorten, most drivers don’t have a spring, and are they fragile.
Thank you .....that was a quick easy fix