And here's my latest "franken-light"! Still needs some finishing but far enough along to post pics.
This one is a no-name 18 volt light that I took a chance on that the LEDS were fine. Got it on half-off day (total $3.50), and a quick check at home proved they all lit. Was scrounging around trying to figure out a battery "pack", and settled upon one of those plastic drill index boxes. Made a great support base, was dirt cheap, and easy to swap batteries. Plus, the LED bulbs have such a low current draw that even well used 9v batteries still work fine! So I use fresh batteries in my other lights, and when the incan bulbs start going yellow, I can transfer them into the LED lights.
I come across pivot head flashlights all the time. Without the battery. Seems like folks who buy a line of cordless tools find out that after a couple of years the maker comes out with a new line of tools - and the batteries don't fit the older tools most of the time. When your batteries go bad or won't charge, the cost of a replacement is too high. So, people toss or donate the old tools.
Enter the flashlights. I can usually get them for a few bucks, and I've figured out a way to wire in 9 volt transistor batteries and get the lights working. Most of the time there's nothing wrong with them - just the battery went belly up. The old Makita stick battery lights were 9.6 volts and work fine on 9 volt transistor batteries. So I hook up 3 or 4 in parallel and get a useful life out of them. 18v are also easy - just two batteries in series. 12, 19.2, an 24 volt lights require some more work. Either a mixture of 9v and AA, or a stack of AA's. Real tough jobs one can always replace the bulb with a 9 or 18 volt variety.