Most of those have the LEDs’ boards pressed in, nigh impossible to non-destructively remove, let alone replace.
When I wanted to scavenge one of those 9-LED boards, it usually means peeling away the “case” ’til the board just pops out.
the battery holder, contacts, springs, etc are all terrible - i wouldn;t do it
Did not realize they were pressed in, but seems reasonable. Do you think it could be pressed out? It would sacrifice the lens and LEDs probably, but I could piece together parts from multiple lights easily.
That’s about 98% of the reason I want to do it. 
===oh
well you will have to fix all that
it is hard because you can;t really solder to the tin plated steel
maybe it is chrome plated
anyway
hard to solder to
i have also seen them where the ‘regulation’ is just one resistor
wle
you may as well go all the way and convert to 1x18650
Would definitely convert to Li-Ion.
For “soldering” to aluminum I’ve done things before like swage a piece of copper in place and then solder to it. But for this light I’m not planning a driver, just click-on, click-off, maybe with a current limiting resistor thrown in if needed.
On the really thin, cheap ones, I’ve never had trouble just popping the board and lens out the front by pushing them from the inside. If you have a Lowe’s Home Improvement store nearby, they have a nicer version with a thick wall, available in various colors. I bought a couple to mod with this board I designed a while back. A good quality 18500 will power it nicely. You just need to sleeve it with a piece of pipe or something so it doesn’t rattle around. I never got my mod completed. I tried it with one of the thin walled cheapies like you have pictured, but I couldn’t figure out how to solder to the inside of the host. Then I never got back to it with the nicer host. I don’t even know what it looks like inside. There might be a shelf. It’s thick enough for one.
Here’s the flashlight at Lowe’s. It’s a Lux-Pro. They have it listed for around $5 online. I can’t remember what I paid in the store.
awesome
I am quite happy with my Varta indestructible 1AAA keychain light modded with a Yuji 5mm. Manufacturer rated for a drop from 9 meters 
Sort-of a non-potted plastic version of the (original) Sofirn C01, only slighty larger. I transplanted the driver from this Varta LED penlight into it, because it drives the LED not so hard. (By the way the Varta LED penlight is a horrible flashlight, horrible light image full of arifacts, the plastic clip broke off right away, crap host construction, but really good battery vampire circuit, even better than the Sofirn C01 or Fenix E01, although it is less efficient it just keeps going on, and on, and on). The drivers of these 2 Varta flashlights are completely identical except for the value of one resistor (50 versus 150). The keychain light with the LED switched to a Yuji is actually a joy to use, even though it is much, much dimmer now. Light output is comparable to a Sofirn C01 (the version with a visible hotspot).
You could also change the resistor value of the Varta 1AAA yourself if you are able to solder SMD components.
By the way these Varta lights are branded Rayovac in the US, for example here is the Rayovac 1AAA penlight.
Most of those I’ve ever seen, regulation is zero. As in, no resistors. It just relies on the internal resistance of crappy hateful little AAA alkaleaks to “regulate” current. That, and hair-thin springs, oxidised contacts, other resistances that add up a little more to limit current.
Figure 9 LEDs in parallel should draw maybe 200mA to be “safe”. So, okay, 4.5V - 3.5V or so leaves 1.0V to drop. In theory.
Realistically, the LEDs get hit harder with fresh cells, but once they start to “wear”, internal resistance increases, so at first you might get 300mA or more through all 9, which’ll drop to 250mA, then 200mA, then progressively less and less as you spend the cells. By the time they’re pitifully dim that you want to swap in new cells, terminal voltage from the 3 cells will be about 3.0V, with the LEDs just barely glowing. So the cells are down to about 1.0V each, which sounds about right.
Naw, most of those LED boards are just a quick swirl of peecee board traces of the 9 LEDs in parallel, no resistor included.
Can’t believe I wouldn’t let this go…
Goggled around, found https://d2ei442zrkqy2u.cloudfront.net/wp-content/uploads/2016/03/MN2400_US_CT1.pdf , so resistance starts out at around 0.25Ω and rises to about 0.40Ω near end-of-life. So figure for a trio of AAAs, that’s 0.75Ω up to 1.20Ω.
A’ight, so that 1.0V drop from above, add in another fractional-ohm to maybe 1Ω total… about 1A total for 9 LEDs? Sounds awfully high, but then again, those lights are impressively bright with fresh cells. So maybe.
Never bothered to measure current on those critters, but it doesn’t really change the fact that most of those cheapcrap lights don’t even bother with a ballast resistor to limit current.
I’ve modded one of the 9x LED lights with Yujis. I’m currently further modifying it with an Nanjg AK-47A driver with guppydrv so I can have multiple modes and run it on an 18350.
I have no idea where it came from - it was a party favor I got several years back. As far as I’ve seen, however, the internal design is pretty much identical for most lights of this style.
I don’t think I would run it direct drive on lithium-ion with Yujis. The design depends on cheap LED’s with a high forward voltage, and voltage sag of alkalines under load.
Like David EF said, you can press the pill out the front from the inside. It takes a fair amount of force, but if you’re careful, all the parts should survive.
The biggest problem with these lights, from what I’ve seen, is the switch. Fortunately, you can press it out by pushing on the rubber switch boot. There is a plastic retainer holding the switch and spring.
The switch I found inside was almost identical to the Omten 1217 that Mountain Electronics sells. I had to file the inside of the retainer a little bit because there were slight differences in shape.
I also roughed up the aluminum tailpiece a bit with sandpaper, to ensure good contact with the tab on the 1217 switch.
For the low current you will want to run, the spring probably isn’t an issue (even a benefit for controlling current on direct drive), although I bypassed mine anyways - this is BLF, after all.
It should work OK if I add in a current limiting resistor though.
you might consider using the twisting as a switch
then you can take out the whole switch mechanism, adding room for the 18650 conversion
wle
If you can find a cheap/free Outback flashlight, they are significantly better made in some ways than, say, most dollar store lights. Boards are still pressed in, but I’ve gotten a couple of free ones like this model with company logos on them.
Their bodies are heavier and better quality than most freebie flashlights. Or maybe I’m just biased because I bike and drive by their HQ all the time. Still wouldn’t buy one, tho.
The threads typically aren’t anodized on these lights, so I don’t think that would work.
I’ve modded one some time ago: Mod of old 9 led flashlight
And found inspiration here: Mule from a 9-LED cheapie and the generosity of BLF members
Good luck
I believe both Streamlight and Princeton Tec have offered multiple 5mm lights in the past. Not sure on current offerings, though maybe ebay would have some old ones from time to time.
i have a outback 9 led and it is definatly a cut above most.
its got ebay hi cri in it now and an 18500.
too bad most are not this good.
it weighs 3 times empty what a hf freebie weighs with its craptastic carbon zinc cells.
I went to Lowes in search of the LuxPro that LB mentioned. I found it, but I also found another $5 light that was a 1/4” longer and fits an 18650 almost straight off the shelf:
It is substantially higher quality than the original cheap junk I had in mind when I first posted this thread, so thank you to everyone for getting me in touch with it.
https://www.lowes.com/pd/FrogLeggs-40-Lumen-LED-Miniature-Flashlight-Battery-Included/50210197
Also, based on recommendations above regarding the Outback brand, I ordered an Outback Tac flashlight that I found on eBay for $7 free shipping:
This one is spec’d longer and wider (and 16led) so it may accommodate a 21700.
Yesterday I bought two Varta AAA indestructible; nice flashlight, something smaller even than a mini-C8, works with twisty and not as I thought with tail push button. I am trying to remove the original pill, to replace the led by a Yuji 3200K, but I’m afraid to force it to break. How can I access the led? Can I remove the rectangular strip of the driver without damaging its reinstallation or the reflector?