Here's my alternative to a solar charger for my boat batteries. It's called a stayncharge, charging system. It charges my batteries by using the left over power from my car altenator, while the motor is running. It charges my batteries on the way to and from my fishing destinations. I've been using this system for over 5 years, with a couple plug updates, and i'm very satisfied with it's results. I'm using the basic model and it's charging 2 batteries for me. I found it to be a good alternative to my solar charger that i attempted to use.