What does duracell manufacture say about the durability of their brand
For the advertising campaign "Trusted evdrywhere", see
http://www.ehow.com/facts_7668667_durability-duracell.html
Their batteries are guaranteed to have a shelf life of seven years. That means they are good that long, if NOT used during that interval.
Consumer Reports testing has shown Energizer batteries of the same type (AA) to power a flashlight about 30 minutes longer that Duracells.