Duracell was cryptic with date codes, until recently. They NOW print the actual date of Manufacture on the package (of both their 7 year and 10 year batteries).
However, this guide is to help you decrypt those packages with 6 digit codes (letters and numbers), so you can determine when they were made and how long they SHOULD last.
The First Digit is the year of Manufacture
the next character (a letter) is the month of Manufacture
the next 2 (numbers) are the day of the month of Manufacture
The final 2 letters/numbers are manufacturing plant (I don't have that list)
For example, to decode "2F11J2":
2 = 2012
F = month, where A = Jan, B = Feb, etc. F = June
11 = day of month
J2 = unknown Plant
Therefore; 2012 June 11 (or June 11th, 2012).
So be a smart consumer and take advantage of the deals you find on Duracell 7-year or 10-year batteries, with cryptic "Date Coding"!!!