After reading all of the problems with that 3.5 gallon heated waterer, I returned mine (unused) for a full refund.
Purchased @3.00 oil drain pan from auto parts store (14.5 - 15.5" wide);
(drilled 1/2" hole 2" from top) of 5 gallon (free) plastic container;
set porcelain light bulb socket $9.99 into 12" cinder block after attaching to outdoor electrical junction box then fitted with 60 watt bulb;
filled 5 gallon container with water, replaced its' top; turned upside down & placed into drain pan(only fills to where hole is in container);
set water filled container and oil drain pan on to cinder block over light bulb assembly.
Plugged it in and it is warm enough to keep water from freezing... Light source of heat is very inexpensive.
Found this idea in BYC learning center
https://www.backyardchickens.com/LC-waterer.html. It works terrific and does not spill if you turn the side with the whole in it away from you (finger on hole) when putting filled container into the oil pan. For 15 minutes and under $15.00 I have what I needed to keep lots of water from freezing - Thanks Again BYC....
Have upgraded from oil drain pan to livestock feed pail 4" deep x 16" wide $9.00... Much easier to place 5 gallon container in wider pail and easier for birds to get beaks into the water for a good drink, water is better insulated than with the smaller oii drain; birds were having difficulty when water was low. Now not a problem. The livestock outdoor pail is rubber, will not freeze nor crack. Much simpler to clean and maintain also. I can bring 1 gallon out and just fill the basin allowing the 5 gallons to be reserve.. Really like this method.