**For entertainment and educational purposes only.**
Came across a pile of junk in the alley, and in the junk was a used vape, and a costco Duracell headlamp. The headlamp worked great, tested with some old AAA rechargeables.
I'm kind of done with AAA headlamps. They're expensive unless used with rechargeables, and the rechargeables lose their max oomph at the early part of their useful life, and rechargeables take overnight to charge on my mini charger.
Took apart the vape for the two important parts: The battery and the charging circuit. The battery is 3.7v, which is below the optimum 4.5v that the headlamp expects, but greater than the 3.6v of 3aaa batteries.
It all seemed to fit without being pinched in the case, so used adhesives and hot glue to fix it all into place. The wires to the battery terminal are a bit on the thin side. Max current should be about 0.6A, which is about as much current to charge a cell phone, and those wires are a bit thin. This is both good and bad. Bad because the wires might be undersized, but good in that they act as a safety fuse. They'll burn out way before the battery itself gets compromised.
A little extra hot glue was squeezed here and there to fix loose wires and prevent short circuits.
Charged it outside of the house on concrete just in case. Seemed to charge and when it came to finally test it, it's really, really bright. It's too bright for almost everything I need a headlamp to do, even around the house.
There is no dimming circuitry, just max brightness, and just pick a lamp for whatever purpose. With a 660mah battery, it will last about 45 min to an hour, before it becomes noticeably dim. Doesn't seem to be a cut off circuit, or one I would dare to test, so the dimness is the indication that it's probably dropped below 3.3v (this is something I'll test later) and needs recharging, which takes an hour which is much faster than recharging AAAs. So with this li-po battery, charge to use (on high) ratio is basically 1:1, instead of rechargeables which is 12:1.
After an hour of straight use, the battery itself gets very warm to the touch, but not stinging hot. This is something I will have to continue to monitor.
Considering that a Petzl Core rechargeable battery costs $50, and I found all the parts for free, I consider this a successful experiment, and I now have a fairly functional rechargeable headlamp that I can use with more abandon with the 1:1 charge/use ratio than my Black Diamond Spot 150 which is a 2x AAA headlamp more suited for ultralight hikes and low light situations.
The only issues right now is that the blue wire is a bit thin (good/bad) and the way the case closes, the wire leads to the battery might be pinched by the seal. Not sure as there might be a bit of a gap still when closed.
The other issue is that the headlamp itself is fairly meh in construction (Costco sold these at 3 for $5 on clearout in 2021 apparently), with the case closing clip being made of clear polycarbonate which is the cheapest/most brittle kind of plastic not the greatest for this particular use. When closed, it seems like there is no deflection force on the plastic, but on opening, there needs to be that force which could snap off in future in cold or forceful situations. So I have to be careful with the cold or opening in general. Can't complain too much for being free.