An Automated External Defibrillator (AED) is a public-access device designed to deliver a life-saving electrical shock to a person experiencing sudden cardiac arrest. AEDs can be used by bystanders without extensive training. The ability of the unit to function correctly depends entirely upon the readiness of its internal components, especially the battery. Maintaining a reliable power source is paramount, as a depleted or expired battery renders the entire device inoperable.
Understanding Battery Lifespan: Standby Versus Operational Use
The lifespan of an AED battery is measured by two separate metrics: its standby life and its operational capacity. Standby life refers to the period the battery can remain installed in the AED, keeping the unit in a “rescue-ready” state while performing regular maintenance self-tests. This duration typically ranges between two and seven years, with many common lithium-based AED batteries rated for four or five years of installed life before requiring replacement.
This standby duration is a manufacturer’s guarantee, assuming the device remains unused and within recommended storage conditions. The other measure, operational capacity, refers to the power needed for active deployment during a rescue. Most AED batteries are designed to deliver a specific minimum number of high-energy shocks, often between 100 and 300, or a certain number of hours of continuous patient monitoring.
A battery’s standby life is immediately compromised the moment the AED is used for a rescue or even for extended training sessions. For instance, a battery rated for a four-year standby life and 200 shocks may need immediate replacement after a single deployment, even if it has only been installed for one year. The high-energy demand of charging the internal capacitor to deliver a shock significantly depletes the remaining battery capacity.
Factors That Reduce Battery Duration
The estimated standby life provided by the manufacturer is based on an ideal scenario, and several environmental and internal conditions can cause premature power loss. Extreme temperature fluctuations, both high and low, degrade battery performance. Storing an AED in an unheated vehicle or an outdoor cabinet in a cold climate can cause the lithium battery to lose power more quickly than expected.
Internal demands also contribute to faster depletion of the battery’s charge. All modern AEDs perform mandatory self-tests, which are automated checks of the internal circuitry, software, and battery power. These self-tests draw a small but consistent amount of energy, and their frequency—daily, weekly, or monthly—is factored into the standby life estimate. Any deviation from the recommended storage temperature or an increase in the frequency of these checks will accelerate the rate at which the battery needs replacement.
Monitoring and Replacement Protocols
Maintaining AED readiness requires a proactive approach centered on visual inspection and date tracking. Most AED units feature a clear status indicator light, which is typically green when the device is ready for use. If this light changes to red, flashes a warning, or the device emits an audible chirping sound, it signals a low power level or a detected fault, requiring immediate battery replacement.
The “install by” date indicates the latest moment the battery should be inserted into the AED to ensure it achieves its full advertised standby life. Similarly, the “expiration date” is the final day the battery is considered reliable, and the power source must be replaced by this date, regardless of whether the device has been used. Keeping a log of the battery’s installation date and its expiration date is a simple protocol to ensure timely replacement.
Electrode Pad Expiration: The Other Critical Component
While the battery powers the AED, the electrode pads are equally important for delivering the necessary electrical therapy. These pads have a limited shelf life, often shorter than the battery’s standby life, typically ranging from 18 to 30 months. The primary reason for this expiration is the presence of a conductive gel that facilitates a strong bond with the patient’s skin and ensures effective electrical transmission. Over time, this conductive gel will naturally dry out or undergo chemical breakdown, even if the packaging remains sealed. Using expired pads with dried gel can result in poor skin contact, which prevents the AED from accurately analyzing the heart rhythm or delivering an effective shock.