I posted this earlier in another thread - really just a bystander here, but I found it quite interesting:
Interesting article from 2008, seems to be saying that the specific type of Li-Ion batteries fitted to customer delivered aircraft differed from those originally fitted to test/certification aircraft:
Boeing looks to boost 787 lithium ion battery service life
Excerpt from above link:
"Boeing will move away from its original lithium ion battery design for its main and auxiliary power units, flight-control electronics, emergency lighting system and recorder independent power supply. Instead, Boeing is investigating the incorporation of manganese inside the lithium ion battery to boost service life.
Boeing has not determined which 787 will be the first to receive the new battery modifications, although multiple programme sources have told Flight's FlightBlogger affiliate that the new battery could be introduced as early as Airplane Seven, the first production 787 scheduled for delivery to All Nippon Airways in the third quarter of 2009."