An externally worn cardiac monitoring and/or treatment system with battery detachment detection is provided. The system includes detachment circuitry and audible and/or vibrational alarm circuitry operably coupled to the detachment circuitry. The detachment circuitry is configured to detect whether the rechargeable battery is detached from the battery-powered externally worn cardiac device by monitoring a connection established between the rechargeable battery and the at least one processor and output a battery status signal indicating whether the rechargeable battery is detached from the battery-powered externally worn cardiac device. The audible and/or vibrational alarm circuitry is configured to receive the battery status signal and output an audible alert in a predetermined frequency range and/or a tactile alert if the rechargeable battery is detached.