Shoot me an AIM message if you can. My SN is Teslawashere.
Well, the only thing that could go wrong is if you do not have a large enough wire, and remember, current will ALWAYS be flowing in that wire, so I would recommend 2 or 3 runs of wire from the battery in back to where the normal battery wires are and do it that way personally. There is no problem, except if you use a normal lead acid car battery, it releases hydrogen gas while charging and under a load, so vent it or get a sealed battery of the sort.