May 2007? That's pretty good. I've burned through a few batteries in the 10 years we've owned our TT. However, I've had my current battery for the past five years; Aug 2008.
I use one (1) group 27 Walmart battery that I bring home after every trip. It lives in the garage, off the floor and on a trickle charger. It's still going strong.
I use my Little Hondas when dry camping so one battery gets us through the night just fine. Ideally I'd like to have a solar charger but I haven't gotten around to buying one. And I may never get around to it.