Apple is extremely secretive about its products.  It has gone to great lengths to prevent news from leaking, even taking the unorthodox approach of killing leaks sites. 

However, it can only keep secrets so long, as its firmware often reveals what loose lips do not.  Apple Insider noted today that the 625K update Mac OS X 10.5.7 for the MacBook Air contains firmware tweaks to the logic board that controls the power functions, thermal management, the sleep LED, and battery.

Apple confirmed that the firmware update was to work with a new series of internal MacBook Air replacement batteries.  Like the previous batteries, the new ones would not be user replaceable, and are only able to be officially replaced by Apple repair depots and other Apple authorized service repair centers.

The company has said it is increasingly using advanced chemistry and adaptive charging to prolong battery life.  The battery design from the MacBook Air has been replicated in the new MacBook Pros.  This in turn has transition the MacBook Pros from having user replaceable batteries, to having much harder to replace internal batteries.  The tradeoff gain has been a substantially improved battery life.

Apple leads the mobile PC industry in battery life, though part of that is thanks to the notebook's EFI (BIOS replacement), which is tweaked for OS X.  Apple has been rumored for some time now to be on the verge of bringing silver-zinc batteries to the market.  Silver-zinc batteries feature a greater capacity than lithium ones and are nonflammable, however, the high price of silver has kept them off the laptop market thus far.