Great question and very important. Philips battery M5070a has a 4 year stand-by life (life while installed in the AED and in stand-by mode). The M5070a 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 your M5070a battery 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". For help keeping track of your AED battery and pads expiration dates please use our FREE online AED management tool, heartsmartpro.com.