While this heater is designed and advertised for aquarium use, I thought I would try usung it for another purpose. At it's price point of less than 15 dollars, I decided to try it out as a small heater for an outside birdbath. The idea being that I could extend the ice free period farther into the winter months. We reside in an area where low overnight temperatures can easily fall into the teens in the winter while most daytime temperatures rise into the 30s or slightly higher.I have for years been unsatisfied with the longevity and safety of the plug in style of 120 volt heaters. I have found that most 120 volt heaters don't last long and they are inherently dangerous to humans and our feathered friends (squirrels too).I tested the Dongker Mini USB heater over a 24 hour period when the outside temperature ranged from 35 degrees to 45 degrees. The freshley filled birdbath water was 61 degrees when I started. Over the course of 2 days the temperature of the water rose 66 degrees and maintained that temp for most of the second day. The homemade bird bath I use holds about 2 gallons of water. The intent was to keep the water from freezing, not to raise to a suitable temperature for aquarium use. I honestly believe this little heater will extend my ice free birdbath season by several months. The result will be that I do not have to remove cakes of ice from the birdbath on a daily basis.So far i am extremely pleased with this economical and SAFE alternative to the 120 volt heaters. As for it's intend use in a small aquarium I am sure that it will work well in that much less harsh environment than what I am using it for. Thanks for a very good product at a reasonable price.