I had the same problem as you. I put a SE 400 on my rail and solved the problem.
I bought mine at a auto store called Pep Boys for about $60, same unit. It doesn't need a regulator because of its output. I always have a charged battery now instead of a partially charged battery. Plus, with the small amp draw we use, the panel makes it up as we use it. About a 1/2 amp.