An intelligent battery having an advance low battery warning for a battery powered device is provided. The intelligent battery comprises a battery suitable for powering a battery powered device and a charge monitor circuit. The charge monitor circuit continuously measures the amount of electrical charge input and output from the battery. When the amount of charge remaining in the battery goes below a threshold amount, an advance low battery warning is generated, wherein the charge remaining in the battery is calculated by subtracting the amount of electrical charge output from the battery from the amount of electrical charge input into the battery. The low battery warning occurs independently of the output voltage of the battery such that an advance low battery warning may be provided for a battery that maintains a substantially constant output voltage until just prior to complete discharge. The circuit also includes an imminent shutdown warning circuit that measures the output voltage of the battery, and provides a battery shutdown warning when the output voltage drops below a shutdown threshold voltage. In a preferred embodiment, the battery powered device is a defibrillator/monitor, and the threshold amount is equal to a selected percent of the battery's capacity plus sufficient charge to provide a selected number of charges to a defibrillator.