I have an M4 that's eating batteries but I love the light. You speak of this conversion to LED and rechargeables (KL6 with 2-17670 bats) for an increased run time but what is the lumen output compared to the stock 225 with MN60 and 350 with MN61? And exactly where do I go to get the conversion parts?
Converting to a Cree (or Seoul) will result in a an increase in output compared to a KL6, and will also get you about a 70% increase in runtime. My estimate is about 160 lumens. While it's not 225 lumens, it's plenty bright. Trust me, I had an M6 that I use the standard lamp on and the KL6 with Cree or Seoul is much more useable. I got rid of the M6 and now use the KL6 in its place. Pick a low Vf LED and you can even run it on a single 17670 or 18650 cell in a pinch. Incandescents are pretty close to dead in my opinion. I don't own a single incandescent anymore.
To convert the KL6, you need the LED of course, and you need some 1210 size resistors to rebias the circuit for the Cree or Seoul. You also need to be able to do surface mount rework soldering. That means a good iron (not a cheap 25W radio shack one), flux, solder, tweezers, and solder wick will also make the job easier. If you don't have SMT experience, you should practice your soldering skills, particularly using a pair of tweezers. I've done this mod for others that do not want to go through the hassle of procuring the parts (the resistors are the hardest to get) or those that do not have the SMT skills.
