A reusable battery indicator includes a voltage sensor, a communication circuit communicatively connected to the voltage sensor, an antenna operatively coupled to the communication circuit, and a connector. The connector is electrically connected to the voltage sensor, and the connector is adapted to be removably connected to a battery, thereby providing an electrical connection between the voltage sensor and the battery. An electrical circuit is completed between the voltage sensor and the battery and the voltage sensor. The connection mechanism includes part of an electrical lock and key assembly.