Goodness, is the cat ok? I dont' know of any heating devices that don't use electricity. Except maybe those cushions that people use at sporting events...where you rumple them up and they give off heat for a few hours. I dont' know much about them or how long they last or anything.
What is the heat for? Just pleasure? Is is constant heat he is looking for because that would certainly require electricity or some sort of fire.
If he just needs it for short periods,here is an idea that we use at home, actually for my niece's "growing pains."
We roll up a dry bath towel and microwave it for about 30 - 45 seconds and then she wraps it around her knee. It stays warm for quite some time actually.

Hope this helps. And I hope the kitty is ok!