Battery required for a portable immersion boiler
You want to get 500W for 10 minutes, plus whatever losses from the water during the heating. Call it 600W for 10 minutes or 60Wh (assuming the water is well insulated and heat loss due to evaporation is very limited). So roughly the size and weight of a big power tool battery pack, and close to the limit for what you are allowed to carry on an airliner. 

Might be useful for situations where open fires are prohibited but otherwise a bit silly compared to a small camp stove, since you'd only get one fairly weakly heated cup of water out of a charge cycle. Kettles draw around 1500 to 3000W (240V land) and still take a few minutes to boil a small amount of water so you may find that estimate on the low side when you actually try to build it. And if you're melting snow, forget it, the phase change eats up way more energy. 

A light (395g) camp stove such as Firefly produces about 2,500W on white gas (8700 BTU/h) according to the specs, and it doesn't take many ml of fuel to do a lot of cooking.