Some friends gave me a souvenir they picked up recently on a visit to Canada. It’s a key-chain carabiner (stamped with “Montreal” and a maple leaf on the side). Opposite the gate it’s hollowed out, and the end is extended, so that there’s a flashlight.
Batteries were not included, so I’m trying to figure out what will fit. It’s rather small. The housing for the bulb (I’m pretty sure it’s a bulb, but the lens is too bulbous to see in and the back side is sealed) screws off the top.
The cavity for holding the batter has an inner diameter at the top of about 9.7 mm. However, there’s a plastic sleeve, possibly to insulate or steady the battery, inside it. I’m guessing that is no thicker than 0.5 mm, so let’s say the battery size is somewhere around 8.5-9.0 mm.
The cavity depth is about 30 mm, although this doesn’t account for the spring, or the fact that it may not be perfectly flat on the bottom. The cap/bulb section has about 6 mm of depth, but at least half of that is threading, possibly more.
There’s a contact bump in the center of the cap. There’s also a patch of solder that’s probably not a contact (it’s raised, but not as high as the center contact) about 5 mm from the center on one side. The outer ring of the bulb assembly is metal, and the carabiner inside sleeve is unpainted, so I’d bet the battery has axial contacts, and it’s turned on/off by tightening or loosening the cap.
I don’t know the answer, but I would bet that plastic sleeve is there to hold a stack of (probably 3) smaller cells, which is a pretty common way to run an LED light, and much cheaper than the high voltage batteries that are needed otherwise.
My first guess was an N cell, but looking up the dimensions online it looks like an N cell would be a bit too thick (about 12 mm compared to your listed 9 mm). Do you know the voltage? An A27 would be 8 x 28 mm. An A27 will be 12 volts but an N cell would be 1.5 volts.
ETA: A27 cells are used in garage openers and key fobs, so they aren’t too rare, even in the U.S.
Unfortunately almost of all of my equipment that’d be useful for testing this thing is packed up in another state. I may be able to at least wire up some other batteries to test what happens at some lower voltages.
One thing I did find - the plastic sleeve popped out while I was messing with the thing (it goes back in pretty easily). Turns out it’s only 15.2 mm long. Also, its inner diameter is smaller than I thought, only 8 mm.
Another note about the cap (bulb assembly). The inner diameter of this area is roughly 11 mm (it threads over the other part). There’s a visible metal ring about 2-3 mm around the edge, where the contacts are.
As for the stacked cell idea - it seems like that would work, but I found that not only can it come out, it can be pushed further in as well, at least 4 or 5 mm. Also that wouldn’t compress the spring much unless they were relatively thick; best I can measure is that the tip of the spring is about 13 mm from the opening. If I stick, say, a AAAA or a pencil in there I can compress it pretty much all of the 30 mm down.
A27 sounds like the right dimensions, but I’ll have to do some testing before I put that much voltage on this.
Played with it a bit more, and it turns out I was able to push on the lens and pop it out. It’s nothing more than an LED on a disk of FR4. It’s blue, and probably wants just a few volts. I got it glowing with two NiMH (~1.2V) that I had handy.
Also, it appears the ring is positive, and the center is negative. That may have some effect since if it’s meant to be axial (as I think it is) the other contact would just be the spring. I can’t remove it, but it looks like the top of it is at least 3 mm in diameter. Although I’m guessing that if it compresses all the way down, it’d be touching the case.