You're lucky, finding a set of batteries for free like that takes a lot of cost out of what is , really, a hobby project.
It happened to me, too, in 2007, when I literally found a pack of batteries far greater than my needs. Since that discovery, it's been a lot easier for me to go farther with many new RE projects, without worrying about how to store the energy. If you really are interested in RE, start simple I say, to learn the basics. Then take on something more ambitious (eg a Piggott 8 foot or a Otherpower 10-foot turbine or a set of solar panels, and the whole project will be easier to complete, because you don't have to fret about the cost of batteries!