I fried the driver on an SK58 (note to self...they don't like 14500's). I ordered a replacement from DX, which was delivered in less than 2 weeks btw, but it was slightly damaged...the edge of the driver was chipped. It still works though, so I soldered it back together. Problem is, I don't know how to connect the outside negative ring to the aluminum pill...I tried a little solder glob but of course it didn't like that. I'm sure I'm missing something, but I'm pretty new at this.
That's quite common.. Aluminium don't like tin and solder. Two possible solution: a brass ring (many flashlight use this solution) or a little hole in the aluminium with a little copper wire in it.
As Davx said aluminium is a bit of a pain to solder (and weld) you can do it though. You want to get as much texture on the surface as you can, so take a file or sand paper and rough up the surface.
As aluminium is a good heat conductor you'll want your soldering iron to be as hot as possible. So if it has settings turn it up to full, if not let it sit and get good and hot for a while before you try.
Some flux will help if you have any.
Another trick to try is applying flux on the area of the aluminium to be soldered, then like Piers mentioned, use a file to rough it up. The idea here is that the flux will prevent the aluminium from instantly oxidizing, and will take a tin much easier.
Thanks for the ideas, maybe I'll try my mini butane torch...with everything else removed from the pill of course. I've welded and brazed other metals in the past but never aluminum, hopefully this will work. I realize I can buy a new light for $6, but I figured this was good training for bigger and better projects.