Amazon claims that all it took was a six month firmware improvement test to get the Kindle 2 to run for 85 percent longer than before, which is a pretty damn impressive feat of engineering.
It also gets a native PDF reader, previously only found in the Kindle DX. The total battery life for the international version measures at seven days with wireless on (up from four days), and two weeks with wireless off (same as before).
It looks like Amazon just improved the wireless usage, which might have come as a result from switching from using Sprint as the provider to AT&T as a provider? Probably not, seeing as previous Kindle users also get the 85% battery life from a firmware upgrade delivered automatically. PDF support comes over OTA upgrade as well, but no timeframe was announced for either. [Press Release]