Using a battery in this design can be viewed as converting electrochemical energy into electricity into heat. Why not cut out the middle man, electricity?
For many year, heaters based on the catalytic conversion of a fuel (sometimes ethanol or methanol) to heat. A quick search led to this flameless, propane fueled heater: **broken link removed**
One advantage to using a fuel is that the "recharge" time is quick and the heat produced per pound is probably going to exceed what you can get with a battery. A little flask of ethanol fuel is easy to carry around, inexpensive, and relatively non-toxic. It doesn't explode like lithium batteries, and it doesn't leak acid or lead salts like lead-acid batteries can do.
You could also skip the whole heater concept and add the ethanol directly to the coffee for a little warm up.
BTW, that Coleman heater is not an example of something you can use directly for coffee. I provide it only as an example of the technology.
John
For many year, heaters based on the catalytic conversion of a fuel (sometimes ethanol or methanol) to heat. A quick search led to this flameless, propane fueled heater: **broken link removed**
One advantage to using a fuel is that the "recharge" time is quick and the heat produced per pound is probably going to exceed what you can get with a battery. A little flask of ethanol fuel is easy to carry around, inexpensive, and relatively non-toxic. It doesn't explode like lithium batteries, and it doesn't leak acid or lead salts like lead-acid batteries can do.
You could also skip the whole heater concept and add the ethanol directly to the coffee for a little warm up.
BTW, that Coleman heater is not an example of something you can use directly for coffee. I provide it only as an example of the technology.
John