It’s getting cold so I’m looking at battery powered hand warmers but I’m not very impressed at any of those available.Do you own one had experience of one maybe even made your own? I’m thinking of maybe making my own but what to power it with? Any advice welcome.
Sanyo used to make hand warmers that used Eneloops.
I used to use Convoy S2/S3s with any type of 18650s, but now I use a Triple from Mountain Electronics and it can actually get to burning hot. Just bring extra batteries… 
Lol I have a ThruNite TN12 2014 and it burnt my finger but I’m looking for something purpose made or maybe make my own.
I wonder if those 2A USB ceramic resistor jobbies would work, hook it up to a 2.1A capable mutiple cell 18650 portable power unit, turn it on, people say those things get really hot…if the resistors were encased in something to hold the heat (more thermal mass) well there ya go…
18650 is the best option for powering a handwarmer in my eyes. 10Wh in a small package, cheap and easy available.
What b42 said isn’t so dumb at all, the most energy gets transformed in heat in a flashlight, you can have different modes, it’s cheap and a small form factor and it can make light too…
I had once a small handwarmer powered with 2xAAs and I sent it back after testing it for a while, got not really warm and eat up batteries. Today I know that alkaline primaries are very bad for higher currents so that might be a reason why I was so upset especially compared to the cheap old style hand warmers with a coal stick inside them.
I have also one of the usbloads, it has a switch to adjust 1A or 2A load and it gets really hot…
Have you seen this: Electronic hand warmers? (Not a flashlight!)
Here is somewhere a thread about this: http://carbonheater.us
I guess a ideal handwarmer has a kind of temperature control, to prevent burning your hands and still warming if it is very cold…
I prefer the lighter-fluid based hand warmers personally...
The chemical snap-type ones work surprisingly well, but the heat doesn't last long, and you have to boil a pot of water to reset them.
I think lighter-fluid must be the best. Last winter I sometimes used one of my smallest 18650 flashlights. They worked fine but had limited run time.
I really wasn’t joking, I use them for hand warmers and lights simultaneously. Even if you dont want light, just put your hand in front of the beam on high on a 2.8A light, you will start to feel the heat instantly. If you really wanted no light, you could run it with your hand on it in your pocket, and the light would be turned into heat on whatever it is focused on as well, plus the heat generated already…you will have a more intense hand warmer than any of the hand warmers they sell like this, except the chemical and fuel burning ones, and for longer than the chemical ones heat for sure. Just dont let it run without your hand on it to sense how hot its getting…
Go to www.monoprice.com and put in 9598 in the search bar. It’s an all-in-one hand warmer, flashlight and device charger.
My wife and I both have one and we really like it. It’s rechargeable, small and really works on all accounts.
We live very rural and it really gets cold here and it has come in very handy a lot of times. Just a thought.