I have a boat and during the winter, the batteries would discharge. Even new ones. Someone told me about this device, and I bought it two years ago and started using it. I started my boat yesterday for the first time in 15 months. The battery provided cranking power just as if it were brand new!Ever since I started using this, I have never had a problem with my boat battery.I am buying another one today for my lawn tractor.If you have a boat or riding mower or tractor, and they sit for periods of time, you must get one of these.For the price, they are a bargain.