Just bought a UF 504B XM-L light from DD, my first 18650 flashlight!!!! Well versed on the safety aspects of 18650's so what do I need to do with the Ultrafire? Any tips? Upgrades? Advice?
just buy a good battery...
I don't have a 504b body, but I do have Solarforces, I would recommend increasing thermal transfer by using cut up soda cans or aluminum or copper foil/feeler gauge material to take up the space between the drop-in and the host. Because of machining variations, there's always some air gap between the drop-in and the host.
Yeah, definitely try to improve heat sinking but other than that, I wouldn't worry too much. It's a cheap light, not a $2000 Titanium uberexclusive custom-built light. This summer, I was using a 504b as a makeshift headlight on a dirtbike for a short while. It was definitely better than nothing and got the job done. It's amazing what you can do if you have a roll of duct tape and don't care about abusing your toys. :D