An Automated External Defibrillator (AED) is a medical device designed to deliver an electrical shock to a person experiencing sudden cardiac arrest. For an AED to fulfill its life-saving purpose, it must be instantly ready for use. The battery is the most important factor in its readiness, so understanding its limitations and maintenance requirements is paramount. This knowledge ensures the device will function reliably when a life depends on it.
The Two Lifespans: Standby vs. Operational Capacity
The lifespan of an AED battery involves two distinct measures: standby life and operational capacity. Standby life is the period the battery is expected to last while installed in the device but remains unused. For the non-rechargeable lithium batteries common in public access AEDs, this span typically ranges from two to five years, though some may last up to seven years depending on the model.
The standby duration begins the moment the battery is installed into the AED unit. Manufacturer documentation provides the precise expected lifespan and replacement guidelines for that specific model. Operational capacity refers to the amount of actual work the battery can perform once the device is activated. This capacity is measured by the number of shocks and the continuous monitoring time the battery can support.
Operational capacity is significantly shorter than the standby life. For instance, a battery with a four-year standby life might only deliver a few hundred shocks or support several hours of continuous monitoring. Any use of the device, even for a brief training session, reduces this remaining operational capacity. Standard protocol requires the battery to be replaced immediately after the AED has been used in a real emergency, regardless of how recently it was installed.
Key Factors Influencing Battery Longevity
Several environmental and operational factors shorten the battery’s expected standby life. Even when the AED is not in use, most modern devices perform regular, internal self-tests. These automated checks occur daily, weekly, or monthly to verify the system’s readiness, and each test consumes a small amount of power. This continuous, low-level power drain gradually reduces the battery’s overall capacity.
Temperature is another significant factor that degrades battery performance. Extreme heat, such as leaving the device in a hot vehicle, accelerates chemical reactions within the battery cells, leading to faster capacity loss. Conversely, very cold conditions reduce the battery’s discharge efficiency, potentially preventing it from delivering its full rated energy during an emergency. For optimal longevity, AEDs should be stored in environments with stable, controlled temperatures, typically between 59°F and 77°F (15°C and 25°C).
Monitoring and Replacement Indicators
The most reliable way to monitor the battery is by adhering to the manufacturer’s printed expiration date. This date, usually stamped on the battery pack, is the final day the manufacturer guarantees the battery’s performance. Even if the device indicates the battery is functional, it must be replaced by this specific date.
AEDs are equipped with visual and auditory signals to communicate their status. A common visual indicator is a status light or icon, where a green checkmark or solid green light signifies the device is ready for use. If this indicator changes to a red “X,” a flashing light, or a warning icon, it signals a low battery or a system fault, requiring immediate investigation and replacement.
Audible alerts, such as a consistent beeping or chirping sound, notify users that the battery capacity has fallen below an acceptable threshold. These auditory warnings are designed to draw attention to the device in unmonitored settings. Maintaining a formal inspection log to track the battery’s installation and expiration dates ensures timely replacement and compliance.
Beyond the Battery: Ensuring Overall AED Readiness
While the battery is a primary concern, the device’s overall readiness depends on other components. The electrode pads, which deliver the therapeutic electrical shock, are a consumable item with a limited lifespan. Pads contain a conductive gel to ensure strong adhesion and effective transmission of the electrical current to the patient’s skin.
Over time, this conductive gel can dry out or degrade, preventing the pads from sticking properly or delivering an effective shock. Electrode pads carry their own expiration date, which commonly ranges from 18 to 24 months, but can be up to five years depending on the brand. The pads must be replaced by this date, even if unused.
Users must be aware of the different types of pads required for patient sizes. Adult pads are used on patients generally over eight years old or weighing more than 55 pounds. Pediatric pads are required for younger or smaller individuals. A regular visual inspection should also confirm the cables are undamaged and the device is free of visible wear.