These flashlights were designed to run on alkaline batteries, not rechargeable batteries. Rechargeable batteries are capable of a much higher current output than alkaline batteries. The switch in the end of the flashlight does not limit the current to below the 3 A maximum limit on the Cree XM-L datasheet.
The flashlight I'm about to disassemble was the victim of such careless behavior as to actually use rechargeable batteries in a Duracell branded flashlight. One click of the button and that was it. The LED was burned out. This feature made for some very unsatisfied customers. Now, for the disassembly.
Update 14 April 2018: I checked out the new Duracell 1000 lumen flashlights at Costco and they now say they work with rechargeable batteries.
First, I'll remove the lens with two strap wrenches.
Next, I'll unscrew the LED module.
Next, I'll pop the plastic off that surrounds the LED. This is the part that secures the LED and heat sink (MCPCB assembly). There is heat sink compound between the MCPCB and the aluminum housing. But this plastic piece doesn't seem to be a very secure or reliable method to make sure the MCPCB doesn't come off the base if the flashlight is dropped.
After un-soldering the two wires, the MCPCB can pop out.
The original MCPCB was part number RB-AL03, made by RAYBEN. It's rated at 0.5 - 0.9 C/W, with maximum operating temperature 110 C.
I looked up a similar LED on mouser.com and found an XML LED for $6.93 each, or $3.24 each for 2000 at a time. I didn't find the same MCPCB available online, but another one for an XML that sells for $1.01 each, or $0.44 each for 10,000 at a time. So it's not surprising that you can find XML MCPCB assemblies on ebay for less than $10 each.
But is it worth it to fix an $18 flashlight? Probably not. Your labor per hour, ordering the parts, and paying for shipping makes it impractical. However, if you could pop in a higher power MCPCB, then maybe it would be worth it to make a custom flashlight. Or, how about a UV LED for spotting fluorescent dye? Or how about a red, green, or blue flashlight?
And, of course, what teardown would be complete without a look at the power button assembly? I used a 17 mm socket and a hammer to push the button out. Then I rotated it counter-clockwise when the ground tabs got up to the threads so that they wouldn't get caught.
Here it is, the power switch board. This is the assembly that cost Duracell so much in product returns. (I have no idea how much.) They must not have realized that you should use a current source to drive LEDs, not a voltage source. Notice that there are no inductors on the board. That means they aren't using a DC-DC converter such as a buck converter. Now, was it worth it to have all those product returns to save a buck, leaving out an inductor? I think not.
Well, there you have it. The power button actually still worked (on my other flashlight) after I re-assembled it.
