deleted BatteryUpdate.bundle. rebooted. ran software update. software update found Battery Update 1.2 (NOT 1.3, which is what had been installed before, and which may possibly have been a leopard-only update that got pushed out to everyone). installed 1.2.
old battery still works. new battery still doesn't work.
it's possible that the new battery is bad, but it seems an unlikely coincidence.
sent a note off to the guys at smalldog.com to see if they have any ideas. if they don't, i guess i'll be making a trip to see the mac sensei in upper darby. or, gods help me, the fine, fine fellows at the "genius bar."