i put fresh charged batteries tonight and the light is so dim… it even dimmer than my C8 
tail cap reading is .65 Amp… anyone know what’s wrong with it?
What kind of batteries?
Trustfire 26650 5000mAh from fasttech
the weird thing is… i used that batteries few nights ago and it was very bright… and even with my other crappy batteries it’s still very bright… but tonight somehow it’s so dim as if it were in low mode
Could be a million things, but very possibly you just have a bad connection somewhere… Maybe unscrew and rescrew everything? (You probably already did)
You’ve checked the voltage of all the batteries? Have you tried isolating the different batteries to determine if it’s one particular battery causing the issue?
Like Chigger said, could be a million things, but the batteries would be the first place I’d check.
I wouldn’t run it for any time with nonprotected cells, but trying GOOD unprotected fully charged cells would eliminate a lot of potential issues.
If you try this it will tell you if its in the tailcap or not if your batteries are ok.
Good advice, you do this when doing an amp check at the tail, if it’s bright then it’s a tailcap issue.
Could be the spring inside the tailcap is damaged or partly melted which is a known problem with this light as it has a high current draw, in particular with 2 cells. Intertwining copper braid around the spring can stop this from happening.
if it’s dimmer than a C8 can u look into the light/led? might have bad/blown drivers? If the LED are glowing like moonlight mode I think the drivers are screwed.
i checked the amp… it’s only .52Amp the dimming issues happened right after i disassembled the headlight from the body.
when i out everything back ( i make sure it’s all tight) and then when i put the batteries back… the high mode is the same bright as in the low mode…
my batteries they all are 4.2V
Have you tried different batteries? Are you using 3 or 2 batteries in series?
i tried different batteries already( all full charged 4.2V ) and i also tried 2 or 3 batteries in series…2 18650s /3 18650s and 2 26650s and 3 26650s but still same result… the light turn on but as if it were in medium mode.
somebody mention maybe i should beef up the spring at the tail cap ( i bought some braided copper wire already)
but before i do that i want to email fasttech first and see what they want to do… if i have to pay to return it, then it’s not gonna be worth it, might as well cut my lost and order another driver?
So with your crappy batteries it’s “still very bright” but just with the 26650’s it’s dull?
no… i meant back then when the light was working normally… even with crappy batteries… the light was very bright.
now … with any batteries it just look a lot dimmer
Have you checked the spring at the driver end? Another thing you can try is removing the bezel and reflector, and see if there is any improvement in brightness. Sometimes if there is too much pressure in the head and it’s pressed down too hard against the emitters it can cause problems, although I doubt it’s causing a short as the emitters are still working.
to be honest … i don’t know what to look at the spring on the driver side…
it has a button( spring covered button) it seems normal… it goes up and down… :~
Have you tried the paperclip trick?
Your a funny bugger scaru. Cant say I beat you at many things but check out post 6.
Oops, I guess I should have read the whole thread first. 
i e-mailed fasttech… and got response in few hrs… they said it’s kinda weird, someone else also have the same problem once they put 26650 batteries on them…maybe it’s too high?
but they’re sending me RMA# and told me to send it to miami office ( they open an office in US already? :D)
and they will send me another replacement right after they send me RMA#…
how cool is that?? now that’s customer service at best!!