Ok, this is interesting.

Per Engadget, an updated model of the US$399 iPad 2 is floating around at retail, and it might improve battery life by as much as 16 percent.

The site is reporting that the lower-cost version of the iPad 2 introduced in March has quietly introduced a new 32nm A5 processor, and that could translate to improved battery life for budget-minded buyers.

The discovery was made by AnandTech, who did an extensive review on the upgraded model, which bears the “iPad2,4” model. Instead of the 45nm process used for the A5 processor used in the original iPad 2 last year, the newer US$399 model features “special A5 chips manufactured using Samsung’s 32nm chip-making process.”

In testing, the website discovered that the 32nm iPad2,4 model boasted improved battery life of 15.8 percent, including a video playback test that lasted 15.7 hours — far better than the original iPad 2 model at 13.3 hours and even the new iPad with its larger battery, which ran for a mere 11.15 hours.

Unforunately, there’s no way to tell which iPad 2 you’re buying until you’ve opened the box and checked the system information.

“This particular iPad 2,4 sample came from Best Buy, and several attempts to find one elsewhere came up short. All indications seem to point to the iPad 2,4 being relatively rare, which makes sense considering what’s inside it,” stated the AnandTech article.

So, it’s sort of a golden ticket that’s out there.

Stay tuned for additional details as they become available.