Alkaline Batteries are good for at least 5 years and I have a Duracell C size Alkaline Battery that is in a Signal Strobe that is still good enough for the strobe to function properly that has a use by date of Jan 98. This Battery is app 17 years old and it still is good. Now how long it will work in the Strobe if I need to use it I have no idea which is why I replaced it just to be on the safe side. I am still keeping the Battery to see how long it will last.

The Energizer Lithium AA Batteries are supposedly good for 12 years and if they are anything like the Alkalines they should last a lot longer then 12 years.

For long term use good rechargeables are a very good investment and they can be recharged with a Solar Recharger.

At this time the best Rechargeable Batteries are NI-MH using the new Sanyo Formulation. Unlike other Rechargeable Batteries these come already charged and ready for use and when charged they hold their charge for a long time unlike other older types.