I bought some 12 volt, 10 watt submersible heating pads/elements to place in the pint size hanging water cups, inside my chicken barn. I wired them into 14 gauge stranded 2 connector wire that gets power from a 12 volt battery charger. The charger is plugged into a thermostat that kicks on at 35 degrees and off at 45. I've got a dozen hooked up for the test run tonight. I could feel the heat when I touched the heating pads with my fingers. I believe it will be enough to keep the water from freezing unless there is extreme cold.
After many internet searches I couldn't find a purchasable heater for something like this...small water cups for chickens.
Some items purchased online for this project...
> Waterproof Silicone Flexible Heating Pad 60*60MM DC 12V 10W
> King Electric IFC12 Ice Free Cube Plug in Fixed Thermostat 120 Volt 15 Amp, 35 45 Degrees, White
> 14 gauge Red / Black 2 Conductor stranded wire
> T-Tap Wire Terminals Blue: AWG:18-14; with Male Spade Connectors