Cold feet and hands cycling below freezing can be a problem .....These overpriced foot heaters over heated and started blinking then shut down, when using the more powerful batteries. I had to unplug them to turn the heat setting down.
More information than you can handle is here:
How to make your own:
This is needed but expensive, and you need pulse width moduators
Product AS636 is a 32-gauge multicore stainless steel wire in a PVC sheath that is only 0.2mm i
As a start, I made a proof-of-concept prototype using half a meter of 20 ohms/m Kanthal® wire and sewing this into the fingers of some thin liner gloves, and driving with the same 3v power source as in the toesties. This didn't work well, perhaps because the heat was distributed over too large an area, so I tried a 9v battery instead, and this was very warm for 15 minutes or so, but then I realised it was drawing 1 ampere, and so drained the battery too fast. Also, the uninsulated wire shorted out in various places, resulting in badly distributed heat, and being single-core it was hard to sew into the glove and had sharp ends that inevitably poked into the skin. Plus it doesn't take solder well.
So I was delighted to discover Cooner Wire who sell every type of wire imaginable, and many that are not. Product AS636 is a 32-gauge multicore stainless steel wire in a PVC sheath that is only 0.2mm in diameter, and flexible enough to sew with a normal needle.
(Feb 2012 - Cooner have removed the product from their web site, but can still get it if you call them.)
The resistance is around 30 ohms/m. Although in principle hard to solder, if you wrap some multicore copper wire around the joint and add a generous amount of solder, you get a very good joint with a normal electronics iron. I don't know how much the wire costs, but probably not much because they were kind enough to send me a metre as a free sample when they heard what I was doing. Unfortunately this was a bit short for a pair of gloves, as 50cm of this gauge has a resistance of 15 ohms, and two 25cm lengths in parallel less than 4 ohms, and my target was around 6 or 7 ohms. I went with the 4 ohm solution, and that was very warm, but two AAA batteries only lasted 30 mins, two AAs 90 mins. If I'd had another metre of wire I could have gotten 3 hours with the AAs, and still reasonably warm.
Still, it seems that there is a fundamental problem with gloves that it's uncomfortable to carry as many batteries as you can tolerate on your feet, and a pair of AAAs or even AAs just doesn't hold enough energy for a whole day. One solution to that is to have cables running up your arm to bigger battery packs, but that's too annoying for my client. An elastic pocket will be added to the outside of the glove's wrist to hold the batteries, and the idea is to use this glove as a liner inside a bigger glove.
I am using GP rechargeable NiMH cells with the following specs :
AAA 850mAh 1.2v =~ 1 Wh
AA 2500mAh 1.2v =~ 3 Wh
PP3 170mAh 8.4v =~ 1.5 Wh