Abstract: A battery and circuitry for monitoring state of charge of the battery are housed in a single housing. A display may be provided for displaying an indication of the state of charge, and a communication circuit may be provided for communicating electrical signals representing the state of charge to the exterior of the housing. Preferably, the battery module additionally includes a switch device for connecting the battery to terminals external to the housing and control circuitry responsive to the monitoring circuitry for causing the battery to be connected to and disconnected from the terminals. The control circuitry operates in accordance with thresholds to prevent deep discharge and overcharge.