Don't. I can't say about Battleground, but the track record for Rasmussen from 2004, even in the final week when they actually try to be accurate since that's the only week customers pay attention to, was pitiful. They missed the spread in State polling by an average of 5%, and leaned slightly Dem in the process (though not as Dem-leaning as SUSA or Gallup).
That said, I recall well that in 1996, EVERY SINGLE POLL was off, and off to the left---in Clinton's favor. Some of them were off by as much as 5%. Obviously, pollsters change their methods every time around, but still, the question remains: are we in 2006, or 1996?