This is a must have for any solar system. Overheating the batteries wears them out or just ruins them. With four batteries costing about nine hundred dollars, each cannot be replaced cheaply. So a $15 part that plugs right into the solar system controller and then connects to the batteries where the controller constantly monitors the temperature and when it detects the temperature is getting too high automatically shuts down the controller system and lets you know. . . is a problem. Ensuring the safety of expensive batteries. It's cheap and easy insurance that I can get for fifteen bucks. Four stars โญ๏ธโญ๏ธโญ๏ธโญ๏ธ!