Philips FR2 battery M3863A has a 4 year stand-by life (life while installed in the AED and in stand-by mode). The M3863A battery has an “install by date” printed on it. The install date is generally 5 years out from the date of purchase. 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 the “install by date”.