is it the advanced key or the standard?
in my speed 6 with the advanced key I needed to have the rear sensor thing replaced twice under warranty. plus I needed to bend the contact in the key a little while back to make better contact with the battery, but thats an 06. i'd say take it in to the dealer either way, make them replace the battery.
by the way, check out the Ohio section, we're a pretty close group that has fairly regular get togethers. stop by and say hi