Recently, Autoline Daily, a podcast I listen to on the way into work, made a claim that 'hybrid battery costs are $6,000'. It took a while to find the sources and I'm not sure I've really got their source but I did come across a 'breakfast' presentation:
http://www.cargroup.org/documents/mcalinden.pdf
I'm not endorsing these charts, just sharing a source. Page 9 is interesting because it shows how 'big auto' sees the price-performance of various technologies to improve fuel economy but one comment.
One of the oldest anti-hybrid claims are battery costs, see page 15, since the first hybrids hit the market. Following inflation (of claims) I've seen anti-hybrid postings as high as $8,000 as battery costs for the Prius. So it is with some amusement to read the latest 'big car' claims bringing up battery costs, again.
Bob Wilson