Hi Y’all. I just had my K40 modded by Vinh. It’s now pulling a lot more amps (6.5) than when in stock form.
Could you recommend me some 18650 batteries to go with it? Also, is it too much of a risk to use unprotected batteries?
I ask this because some of the fatter 18650’s make it a really tight fit in the battery tube. I’m using the Panasonic 2900mAh ones at the moment and wondering if there are any better alternatives.
Would appreciate any help. Cheers 
The really important question is, what does the mod do to the battery? Only Vinh can answer that.
If it provides its own protection then why would you need a protected battery? Your charger should prevent overcharging (the real threat) and the mod should likely shut off at some “not undercharged” level. That’s assuming you can stand to leave the battery in the torch for that long! “Dim” is only “good” when it’s followed by “bo”…
“Undercharging” won’t likely be a problem if you never go there.
Six-and-a-half million micro-amps, though… That’s close to 3C for some batteries; nearly 2.25C for yours. Do they make a 3250mAh 18650 yet? There are many 18650s that won’t flow that much current. You’ll notice how dim it is. The mod will probably throttle back (doesn’t that sound nicer than ‘attenuate’?), but this is one place a protection circuit could help. I think it’s quite possible the demand will just cause it to fail open and “kill” a perfectly good low-current battery, but that’s not really a bad thing if you don’t try to smell it.
6.5A? You might have something bright enough to be interesting. If it were me, I’d worry more about the ability to deliver the Big I, than whether or not it had a protection circuit.
BUT… I’d contact Vinh to be Quite Sure before I stuck the first battery in it!!! I may be Dim, but…
I just run Keeppower protected 3400mah cells in my K40vn. Works awesome in the light. Mainly you just want a decent battery, Panasonic core is best. Not sure if I would do any “hot” batteries like 20R’s and such, for fear of boosting the lights amps even more. It’s high enough as it is.
Unprotected should be just fine. Obviously keep track of them to prevent over discharge with the higher amp draw this light creates.