The Philips HeartStart battery has an operating time of 4 hours or a minimum of 200 shocks. The shelf-life of this battery five years, and will last four years from the time of installation.
The HeartStart AED will indicate when the battery is low by using both an audio alert (a chirp) and a visual alert (a flashing i button). Once the new battery has been installed the AED will stop chirping and the indicator light will start blinking green again.
Philips HeartStart OnSite