Great question and very important. Powerheart battery 9146-302 has a 4 year stand-by life (life while installed in the Powerheart G3 AED and in stand-by mode). The 9146-302 battery has a "manufactured on date" printed on it. This means you have a 5 year shelf life (new and uninstalled). So the expected expiration date is 4 years from the date you install your battery as long as you install the battery within 5 years of the manufacture date.

This Cardiac Science Intellisense battery (yellow) is a non-rechargeable battery that is compatible with Powerheart AED G3 models, 9390E, 9390A, 9300E and 9300A shipped after April 12, 2004.