Just received the HK4S awhile ago.
Apparently this is a 26800 flashlight.
By default, it comes with a short tailspring (really long body tube).
Using unprotected flat-top 21700 battery (eg. Vapcell G50 21700), or even a longer protected 26650 (Keeppower), the tailcap spring will not make contact at all with the flashlight.
With the default short tailspring, I could only have the flashlight make contact when I use a protected 21700 battery (I have one from Rofis MR30).
(unfortunately, I do not have a 26800 battery. I do have a 26700 LiFePO4 battery which I bought for ‘testing’ only — and just like the unprotected 21700 batteries, it won’t make contact with the default short tailspring)
Fortunately, the accessories package does include a longer tailspring, which means the short tailspring has to be pried out (I thought it was difficult to pry, but it pried out easily), then replace with the long tailspring. Now the flashlight works with regular unprotected/protected 26650 batteries or flat-top 21700 batteries. Now I wonder if just plugging in the long tailspring in the tailcap will have good contact resistance?
using these 4 different batteries to test if they will make contact with the HK4S body tube
(protected 21700, unprotected 21700, protected 26650, unprotected 26650)
notice there is a big clearance/gap when using unprotected 21700 & unprotected 26650 (short tailspring will not make contact on the battery at all)
using a protected 21700 will make contact with the short tailspring, there is still some clearance space (will probably fit the 26800 battery type, mentioned in the included manual)
difference of the default short and long tailspring (default short tailspring installed; long tailspring included in accessories pack)
forgot to mention, the positive side (head/driver) is a big copper button instead of a spring.
~
other note: it uses a somewhat old version of Anduril:
- no 15-clicks version check
- no factory reset
- has manual/automatic memory mode toggle (estimated Anduril version is 2019-06-02)
- has 2-level brightness when in lockout mode