Safety in RC is a bit different from flashlights. RC you can blow up the bugger with enough smoke as if you lit up a 100 shot fireworks cake and no issue, coz it is outdoors and not in your hand. But a flashlight is often in your hands, plus it is enclosed tightly plus extremely securely (a good tube of 6061-T6 is tougher than you think).
Nice :) But high current cells usually don't do this without reason, if they do at all. Remember I charge all my batterries at home :) So it is not always outdoors :) My transmitter is lipo powered, I even use liion cells at home to power up home devices. Killed many cells, they always warn you something is wrong.
Yep, for you since you are in RC, you'd have at least the basic skills and equipment to test and monitor. Charging, discharging, testing is a side-line hobby by itself for some of us. Check out old4570/mitro/HKJ's work. But the true is, I think 98% of us here don't even have a basic DMM or lux meter.
But this and good chargers should be something normal. You see what is wrong with cells every charge if you have at least resistance measure and simple thermometer. Past data you can even collect yourself if your charger can't. If you want to say that one light is 5% stronger, it is hard to see with your eyes, you need a meter.
I don't like idea of objects which can make a shortcircuit inside flashlight, can;t you weld some material on cell plus to make it higher? Of course many people use magnets and it works, but it is not safiest method in my opinion :)
King Kongs do not work in 3x 26650 as-is. These cells have a bit of a recessed positive contact and in order to make a connection between the cells enough force has to be applied to squeeze them together. You can fix this in a number of ways, but AS-IS they don't work. I have not tried 2x26650 yet.
I have some IMR BatterySpace 26650s from a while back and they DO work in 3x26650. these cells have a bit of a raised button on the positive end and it enough to make contact. However, connection can easily be easily interrupted with a slight bump. (The good news is that it takes more than a bump to change modes.)
So unprotected cells will most likely require adjustment to work properly. I'll report back later.
EDIT: The positive contact inside the flashlight is either flush with or recessed in that white collar you can see in the pictures, so no matter how much pressure you put on the cells it's not going to make contact. The head either need a blob of solder, a magnet (at your own risk),or a heavy spring. Even then, with the KK cells you are most likely going to need solder blobs on the positive ends or magnets between the cells. On mine, the force required to make a connection between cells is so great I don't think it could be done reasonably. (Think old D Maglite spring levels of force).
it is basically conductive adhesive but in a much nicer dispenser than a jar. it costs half as much at radioshack and you could do a few hundred batteries. Store it tip down or the tip dries and clogs.