Abstract: A safe, low-cost battery monitor and control system is presented. Electronic modules are connected to the terminals of respective batteries that make up a series string. Each module produces a go/no-go signal for each of four battery conditions: over-voltage, under-voltage, over-temperature and float-voltage, which are read by a network controller connected to each module via a single three-wire local area network. Based on the information received, the controller can adjust the charging current to the string, terminate the charge cycle, limit the current drawn from the string when in use, or disconnect the string from the system it is powering. The controller can record a history of the charge and discharge activity of each battery, so that the weakest batteries can be identified and replaced instead of scrapping the entire string.