I found this two month old thread while searching for my topic on mailing lithium batteries.
Basically I ordered a bunch of stuff from TCSS to be sent to me in Australia. The package was marked as shipped, but a few days later I got a note from Tim saying that USPS has returned the package as the li-ion batteries are no longer accepted. So he's removed them and refunded me on the batteries.
He's posted on his forum that USPS has now cracked down on battery shipping, and now on his website, all his batteries are marked as not available for international shipping. :'(
Reading Australia Post's website, their rules state that we cannot post batteries out internationally, but domestic is allowed but only by road. It's possible that Australia Post is not even accepting air carried batteries into the country, regardless of carrier. My guess is that since parcels arriving from overseas are via air, then this would not be allowed since the plane would be entering Australia.