3w Luxeon led

I got these cheap lights on ebay to see if I can mod it with a brighter emitter but I tested the stock led with a 3v cr123 battery and it got considerably brighter. The battery it supposed to take is a single 1.2/1.5 AAA. What do you guys think about putting in a 10440. Either way I will probably try it anyways the light cost me only $2 n something. Light is well built but not very bright maybe someone here tried this already and can give me some good advice before I blow it up. HEHEHE

If you already have the 10440 cell, discharge it a little to get it down to 4.0V at least, then put a multimeter in series to measure current consumption between battery end and tail threads (Or wherever this light allows for battery-driver current measurement). If current consumption is above roughly 1A, best to immediately stop the test and conclude it is using too much power at 4V, let alone 4.2V.

If it isn't above 1A current, charge up battery the rest of the way and repeat the test, again much above 1A could be a problem and the test should be aborted.

If you have no Li-Ion cells to test with you could discharge a regular NiMH to ~ 1.0V/1.2v second test, and hold it in series with the CR123 cell to approximate the voltage of the above proposed tests... but as you wrote, they don't cost so much to be worried about but a working flashlight sure beats a dead one and the tests are pretty quick and easy.

no wonder that the heavily overdriven emitter gets brighter
(any modern emitter would do the same, with the difference that it is at least double the brightness)

For a few bucks more You get comparable lights already with Cree or Seoul inside at Kaido, or DX, or ...,
so in the end cheaper and better made, than when modding these

I'm just learning how to mod them for fun. I think it is interesting how this all works. Not really about the money and how much it cost.