If you can't find them, I have had some success making my own insulated water buckets-can't claim coming up with the idea, but it at least delays the water from freezing for quite a few hours.
Take a 5 gal bucket and wrap both sides and bottom with a layer or two of bubble wrap. Then duct tape completely over all the bubble wrap- both bottom and sides. Fill about 4 gallons with water and add to the top a gallon of hot water. This has worked in my barn with temps in the teens overnight-maybe a light layer of ice forms, but the bucket has never frozen solid.
Word of warning-mouthy horses may play with the duct tape, so I wouldn't recommend in those cases-but I haven't had a problem with that so far.
I'd think that would be an extraordinarily difficult feat, given the fact that regular batteries don't work optimally in the cold and are also really inefficient at making things hot. Love to see the product, though.