I can’t promise you anything. But I personally wouldn’t worry at all about the current that 3x LR41 button cells could send to this LED. 
At least, given usage time is 3 hours. Must draw something less than 25 mA, given a capacity of 25 to 33mAh each cell. If my math is ok, that is :+1:
A lot less than 25mA on average, this is for sure. The actual power delivery efficiency is quite low, such cells aren't designed for high drain. Simplicity and reliability are the main factors here.
If you need 'em cheap, check this ad for example: https://www.ebay.com/itm/10PCS-1-5V-AG3-LR41-392-SR41-192-Alkaline-Button-Coin-Cells-Watch-Battery-Sturdy/382209158751 :-)
They’re powered by three LR41 alkaline button cells. The 45 lumen stock rating strikes me as extremely unlikely.
Those cells can’t push much current. I don’t expect it would be any problem.
Hey, thanks. Yes, that’s what I was thinking, but you never know.
Even the “half watt” LEDs can’t reach 45 lumen output. They are generally only rated up to 100mA @ 3.4V, which would translate to 0.34W of power. To get 45lm out of that, you would have to be getting over 130 lm/w efficiency, which none of these LEDs have. The cheap LEDs in this format are only good for 20mA current. Perhaps they meant 4.5 lumens? That would actually be the likely output of standard LEDs in this format.
Well, that usually is their rating. Months ago I did some testing on a bunch of 5mm and 10mm leds I had lying around, bought in 2006 or so. The 5mm ones would start dieing at 140+mA, and the 10mm ones slightly higher at 180+mA if I recall right.
So, they could be hard driven to some extent (100+mA pulse driven successfully).
It is the same keychain light as the Astrolux TB01, that had a bit different type of 5mm led than usual, with extra thick leads. I never measured the output before modding it but it could have been 45 lumen (so maybe 120mA).
I would like to get some of these LEDs when you get them restocked. Thanks.
So, Barkuti and djozz, are you guys implying that the light in question is actually using a “half watt” LED and overdriving it, in order to get 45 lumens out of it? That would be a strange thing to see. Can somebody test one to find out what the output really is? I’m really curious now.
45 lumens from a 5mm led when driven by 3x LR41 cells? LR41 alkaline cells have very high internal resistance. An alkaline AAA with close to 1000mAh features ≈0.22Ω of IR with little use (Duracell Plus Power AAA at the ≈150mA x-axis point, 0.5 - 1A discharge curves). A cell with less than 1/30th of such capacity would have 7+Ω of internal resistance in the same conditions, which at 100mA of drain/driving current is a drop of 0.7+V for a single cell and 2.1+V for 3 cells in series, this means no chance of hard driving the emitter even with fairly new cells. According to these figures, those 45 lumens are a blatant exaggeration or typical false advertising. 
Thu, 09/19/2019 - 23:42; Fri, 09/20/2019 - 15:30; edited for clarifications.
Won’t ship to Germany but thank you :-).
Or this other one with a different brand: https://www.ebay.com/itm/10pcs-Lot-AG3-SG3-LR41-192-Alkaline-coin-Button-coin-Cell-Battery-Suncom-New/191977303038
Yes, got a couple of them :+1:
Update: The next shipment is said “out of delivery”, but this is very late in the day where I live and the courier has not arrived.
I will put the worst-case scenario that the next shipment will arrive on Monday.
i would be interested in a pack of these LED’s when you restock them — thank you.
Some additional potential host options.
The Red Cross Blackout Buddy emergency light (link to confirmation of modification), so you can have a warm white auto-on power outage light. Takes 3 emitters, I think.
The Red Cross Clipray is similar, but instead of a power outage light, it is a handcrank one that can run either lights, or supposedly charge USB devices (slowly).
The Coghlans dynamo flashlight is a very small crank light with 2 emitters. It seems like a good kids flashlight if it can hold up.
I would love to participate but don’t know how to use these emitters. Do they require soldering? Also which flashlight host can these go into?
^soldering is required. You will find LED similar to these on keychain lights, or some other flashlights discussed earlier in this thread.
There is also an interest list by Djozz for C01 host, but I’m not sure if its ever going to happen.
Which not? 
There have been some mentions here: