More accurate would be to determine what the margin of victory was in the battleground states in 2008. It’s possible that it might have been closer than the national spread of 7.27%.While it's called "Battleground", the 47-47 tie in the poll is actually across the entire nation, not just in the battleground states, so the 7% comparison (to the 50-40 margin) is the right one.
This is a battleground poll for 10 states:
The Battleground tracking poll has been performed nationally each week. POLITICO considers the 10 competitive battlegrounds to be Colorado, Florida, Iowa, Michigan, Nevada, New Hampshire, North Carolina, Ohio, Virginia and Wisconsin. Taking just those states and adding them up from 2008 I come up with 7.08% advantage for Obama, nearly the same as the 7.27% national advantage.