Reddit reviews Portable Water Heater Coil Aluminum Hot Water Heater (1000 Watts) by GCG

There are these USB/plugin hot plate cup warmers out there, but i haven't tried them myself. https://www.amazon.com/Mr-Coffee-Warmer-Office-MWBLK/dp/B000CO89T8/

There are also immersion heaters designed to heat contents of a cup. I also haven't tried it myself, but always tempted to buy https://www.amazon.com/Portable-Water-Heater-Aluminum-GCG/dp/B00PFZFK78/

I'd use a vacuum stainless steel flask. That would be less work and less energy used as you'd only have to fill it once.

I imagine something like this would do the trick. Off flavors from the aluminum should be minimal. It certainly isn't as cool as the iron rod though.

Out of curiosity, what makes that heater better than the cheap sub-$10 ones like this:

https://www.amazon.com/Portable-Water-Heater-Aluminum-Watts/dp/B00PFZFK78/

Seems like the additional wattage is unlikely to do that much unless it's being used for actual boiling...?