Lithium manganese dioxide (Li-MnO₂) batteries are primary batteries, meaning they are non-rechargeable. They generate electricity through chemical reactions, using metallic lithium as the negative electrode and manganese dioxide as the positive electrode. The adoption of disposable Li-MnO₂ batteries (non-rechargeable) in Automated External Defibrillators (AEDs) stems from specific technical requirements and real-world application considerations.

An AED is an emergency medical device that typically sits on standby for extended periods, potentially years before it is ever needed. Li-MnO₂ batteries feature an extremely low self-discharge rate; even after years of storage, the battery retains most of its capacity. This guarantees that the AED can activate reliably in critical emergencies without frequent battery replacement or concerns about power depletion. In contrast, rechargeable lithium batteries suffer from higher self-discharge and shorter standby duration. They require regular recharging within short intervals. Since AEDs may remain unused for a very long time, maintenance staff are likely to overlook charging. If the device runs out of power during an emergency, the consequences could be fatal.

AEDs are deployed across public spaces with low-frequency maintenance schedules. Using disposable batteries eliminates the hassle of periodic charging or replacement, and reduces the risk of device failure caused by neglected charging.

In addition, Li-MnO₂ batteries offer high energy density, storing substantial energy within a compact form factor. To deliver defibrillation shocks, AEDs need instantaneous high voltage and high current output (realized via built-in capacitors). Li-MnO₂ batteries provide stable energy supply to meet such sudden high-power demands — this is also why ordinary alkaline batteries are not selected.

The choice of non-rechargeable batteries for AEDs also reflects design priorities centered on safety and performance reliability. An AED is life-critical equipment, and its battery must perform flawlessly when emergencies strike. Disposable Li-MnO₂ batteries require no charging, avoiding performance degradation stemming from improper charging, battery aging, or repeated charge-discharge cycles. Battery performance directly correlates with the functionality of an AED. Rechargeable lithium-ion batteries lose capacity after numerous charge cycles, compromising long-term reliability.

Li-MnO₂ batteries have another key advantage: a wide operating temperature range and stable performance under diverse extreme temperature conditions. AEDs may be placed outdoors, inside vehicles, or in locations with varying climates, so batteries must adapt to these environments to ensure readiness at all times. While Li-MnO₂ batteries carry a higher upfront cost, when accounting for maintenance and replacement expenses associated with standard lithium batteries and ordinary alkaline batteries, they deliver the optimal balance of cost and practicality.

Why There Is No Uniform Standard for AED Battery Sizes and Interfaces
At present, AED batteries vary widely in capacity, performance and connector interfaces, due to multiple design factors:

First, battery capacity readings are estimated by the device’s Battery Management System (BMS). The accuracy of capacity estimation depends heavily on a manufacturer’s experience with such medical equipment. Modern lithium battery devices are equipped with a BMS, which calculates remaining power by monitoring voltage, current and operating duration and displays it as a percentage or numerical value. Since this is merely an estimation, many manufacturers adopt conservative algorithms. For life-saving AEDs, battery readings can deviate significantly due to ambient temperature fluctuations. Inaccurate power calculation — such as displaying sufficient charge on an already depleted battery — creates severe operational risks.

Second, different devices adopt distinct interfaces. Some use traditional Pogo Pin (spring-loaded pin) interfaces, the same type found on older universal mobile phone chargers. Under certain operating conditions, these interfaces risk intermittent poor contact that triggers repeated device restarts and unnecessary power loss. Blade-style battery interfaces offer tighter connections and superior stability, albeit at a higher cost.

Third, AEDs differ in battery compartment layout and overall dimensions, resulting in batteries of varying physical sizes. Achieving unified specifications in the short term poses significant challenges.