An external medical device includes a battery that can support a plurality of charge-discharge cycles prior to a predetermined battery life threshold. The device also includes a battery circuit that is operative for monitoring a condition of the battery, determining a battery life status of the battery based on the monitored condition and the predetermined battery life threshold, and, responsive to the determined battery life status, causing the device to enter into a low power operating mode. The low power operating mode can include modifying device functions that are performed, or modifying the manner in which a capacitor of the device is charged, or changing the battery that charges the capacitor, or isolating the capacitor from charge drainage, or causing the device to operate from charge stored on the capacitor.