I’m looking to use a few spare SK68’s running 14500’s as hand/pocket warmers - one is currently sat in front of me whilst I test it to see how long it’ll run for, but if it’s long enough then there’s certainly enough heat. If anything maybe a touch too much - I’ll consider the option of running it of Eneloops instead, but for now I thought it might be an idea to wrap them in something that’ll even out the heat distribution. Any household goods spring to mind that would fit the bill?
I don’t think there is anything that will do what you are seeking. It sounds like you are saying the light only gets hot in one area and you would like to spread the heat out more along the tube.
The only way to do this would be to trap the heat in the tube, slowing it’s dissapation.
This would be bad for the led, the cell, and difficult to get the heat to come through whatever material you wrapped it in.
Perhaps you can get yourself some actual handwarmers. These are pretty cheap here in the US and sold at any sporting goods store. 
Yup. The accelerated-aging test of li-ions heat cycles them. Heating them up is not a good idea.
If you want a handwarmer, route the power through an electrical resistance element — a battery powered heater is a good idea.
A hot battery used as a heater is not.
Remember those vents on cells? They’re there to spew out the innards before they get hot enough to self-ignite.
Just rub your hands together.
The ‘made for task’ handwarmers and the like are too expensive or too cumbersome with wires running everywhere. Was looking for a cheaper, simpler solution. The disposable type aren’t cost effective (I spend a lot of time outdoors) so something electric makes sense but I’m not seeing anything worthwhile without spending more than I’m willing to.
I got an hour out of a 14500 so that’s a no-go anyway, but everything you guys have said does make perfect sense.
Back to dressing up like the Michelin man…
Wires?
I got 5 of these last year
https://www.amazon.com/gp/product/B00965V752/
and they’re great. The gf loves them, I love them, and they double as doodad-chargers in a pinch with the included cable.
I keep them in each hand in my pockets, but if you want them in gloves, make sure the gloves are loose enough to fit the donk. Never had them on long enough to run them down, so I’m not sure how long they last on one charge. The blurb says 5hrs and 6.5hrs.
I got mine a bit cheaper, maybe because it was towards the end of the season, but they’re definitely worth it.
—
Nb: the disposable ones can pop open and leak nasty nasty rust powder all over what they’re in (pocket, glove, whatever).
Never tried the butane ones.
I think your much better off with the old school hot hands, or you can get some electric handwarmers that have a couple of 18650s in them.
On the off chance it’s of interest to anyone, after more trawling I came across something that looks both cheap and fairly fit for purpose:
Been playing with them today. Nice solid heat, worn under an insulation layer and a midlayer they were almost uncomfortably warm. Might see about a way to get them heating more evenly (some sort of heat reflective material to warm up the layer of air under an insulation layer?) but I’m pretty happy with them so far. Especially at that price.
Looks good, will have to get a couple of these.
When you say they get almost uncomfortably warm, was that with layers of material between the pad and the skin or with it directly in contact with the skin?
With a fleece and base layer between the warmers and skin.
I bought a few(4~5) of those from ebay for $1 each last winter. Even being very careful in using them they all perished in one season (bad solder joints & there is no restraint against tugs going directly to the joints.)
That said I found them to be good while they lasted. Afterall for a dollar one doesn’t expect these to last a lifetime, right? I have no complaints about using $4~$5 for hand warmers for a season. Heck even the fuel for those lighter fluid hand warmers probably cost me that per season. & I do like using these simple USB ones much more. So much more convenient.
AZ
Needs moar microcontroller! 
Shouldn’t take much to whip up a driver board for these with variable duty cycle.
And by “shouldn’t take much”
I mean not much more knowledge than the amount I don’t have. :nerd_face:
You could try a peltier module — this is an example, from a known good source, not expected to be the budget or cheapest choice:
I love me some microcontroller as much as the next guy, and a peltier module sounds like a fun project - if you can plug it into a 12 Amp Hour battery. (Seriously, those things just EAT amps.)
I was doing some electronics work last year in a large building renovation where they did not have the HVAC system running. Detailed work that precluded gloves and left my hands too cold and stiff to actually do the work. So I went to Walmart and bought an old fashioned Zippo catalyst hand warmer for 14 bucks and a bottle of lighter fluid. Lasts for 8 to 12 hours and worked really well. I found that if I put it in my shirt breast pocket it felt like my whole body was warmer. Dunno if that was psychological or truth, but I guess it doesn’t really matter.
It worked for ol’Grandad, and it makes me smile when I light it up.