|MadSci Network: Physics|
There is current in a galvanic cell, even when not part of a circuit. This leakage current exists in any battery and will eventually cause an unused battery to go dead. This is one of the reasons battery manufacturers now commonly put a “use by” date on packaging.
Leakage current can be minimized, but never completely eliminated. The manufacturer accomplishes this through the battery design. The user can also affect this through storage; storing a battery in a cool place slows the chemical reaction.
Try the links in the MadSci Library for more information on Physics.