A simple, inexpensive and easy to install device designed to protect your batteries from overcharging when you are using your RV for a long time. I don't understand why you just can't integrate this into all progressive dynamics charging converters that are standard on new motorhomes. How much could it cost extra $5? No wonder the motorhome industry in this country enjoys a well-deserved reputation as a company that mostly strives for the lowest common denominator!